1. INTRODUCTION Arsenic, Iron & Fluoride are considered to be the most harmful pollutants in water bodies. The growth of these contaminants results in severe adverse impact on human health, to overcome this issue we look into the solution of these contaminants (Haldar et al., 2020). The major source of arsenic contamination in groundwater is associated with the geogenic origin. The contamination of groundwater also results from several anthropogenic activities, such as geothermal discharges, mining, agricultural activities, medicine, feed additive, landfill leachate etc. (Yadav et al., 2021). Arsenic is a carcinogen and its consumption has an adverse effect on gastrointestinal tract, cardiac, vascular and central nervous systems. Arsenic can exist in various chemical forms, including inorganic or organic, in combination with other elements. Inorganic arsenic exists in three main valence or oxidation states: As(0) (metalloid arsenic; 0 oxidation state), As(III) (trivalent state; such as arsenite), and As(V) (pentavalent state; such as arsenates) (Hou, 2017). Arsenic concentration is majorly found in the countries especially Argentina, Bangladesh, India, Mexico, Mongolia, Thailand and Taiwan, were arsenic concentration from 100 to over 2000 micrograms per liter (ppb) (Ning, 2002). The chief natural source of fluoride in soil is the parent rock itself. Fluorite, the only principal mineral of fluorine in nature, occurs mostly as an accessory mineral in granitic rocks. The granite rocks contain fluoride concentrations of 20–3600 ppm (Ayoob & Gupta, 2006).Fluoride is responsible for affecting the calcium present in mineralized tissues. Too much fluoride can lead to dental fluorosis or skeletal fluorosis, which can damage bones and joints. The countries like India, China and parts of Africa have seen a widespread problem with fluoride-rich drinking water. The highest fluoride contamination in the selected countries (India, Mexico, Pakistan, Egypt, Ethiopia, Saudi Arabia, Niger, USA, Senegal and China) (Kumar et al., 2019). The deterioration of groundwater quality is a major concern. Arsenic and Fluoride are two important contaminants of groundwater in varied regions of the world. The major countries facing the issue of arsenic contamination are East Asia and South-East Asia. In India, the worstaffected regions include the Gangetic plains of West Bengal, Ganga plains of Uttar Pradesh as well as Bihar(Jha & Tripathi, 2021). 1 Iron is one of the most troublesome elements in water. Rainwater as it infiltrates the soil and underlying geologic formations dissolves iron, causing it to seep into aquifers that serve as sources of ground water. Although iron is an essential mineral for human, its presence in ground water above a threshold level make the water unusable (Beenakumari, 2009). The presence of iron is an unexceptional water problem in faced worldwide. It causes unpleasant metallic taste, discoloration, straining and high turbidity are some of the problems associated with its presence in water(Silva et al., 2018). Since decades, there were several technologies for the removal of arsenic, iron & fluoride from drinking water such as Electro-coagulation, reverse osmosis, precipitation, membrane based filtration, ion-exchange, photochemical oxidation and adsorption techniques are effective and efficient methods for the removal of arsenic. Among these adsorption processes are preferred over to other methods due to their convenience, easy operation and eco-friendly (Haldar et al., 2020). Table 1. Range of Arsenic Concentration in Groundwater in Different Parts of India (Central Ground Water Board, 2019) States Andhra Pradesh Assam Bihar 2 Districts Guntur Kurnal Nellore Golaghat Jorhat Jorhat Lakhimpur Nagaon Nagaon Nalbari Sibsagar Sonitpur Cachar Begurasai Bhagalpur Bhojpur Buxur Darbhanga Arsenic Concentration( mg/l) 0.01-0.02 0.02 0.03 0.01 0.01-0.02 0.1467 0.02-0.04 0.055 0.01-0.02 0.02 0.02 0.01 0.065 0.01-0.05 0.01-0.03 0.01-0.05 0.02-0.04 0.01 Chhattisgarh Delhi Daman & Diu Gujarat Haryana 3 E.Champaran Gopalganj Kathir Khagaria Lakhisarai Lohardaga Madhepura Muzaffararpur Purnea Saharsa Samastipur Siwan Vaishali W Champaran Godda Dhanbad Rajnandgaon Rajnandgaon Rajnandgaon Rajnandgaon Rajnandgaon East Noth-East Diu Amreli Anand Bharuch Bhavnagar Dahod Gandhinagar Kacchh Mehsana Patan Rajkot Surendranagar Vadodara Bhiwani Mahendernagar Palwal Rohtak Sirsa Sonipat Ambala 0.01-0.04 0.01 0.01-0.04 0.01-0.04 0.02-0.05 0.01 0.02 0.04 0.01-0.02 0.01-0.05 0.01-0.04 0.02 0.01-0.04 0.01-0.02 0.06 0.057 0.01-0.05 0.095 0.071 0.053 0.09 0.02 0.01 0.01 0.02 0.01 0.01-0.03 0.01 0.03 0.02 0.02 0.02-0.03 0.01-0.02 0.01 0.01-0.02 0.01 0.01 0.01 0.02 0.04 0.02 0.01 0.058 Himachal Pradesh Jammu & Kashmir Jharkhand Karnataka Madhya Pradesh Odisha Punjab Rajasthan Tamil Nadu Telengana Uttar Pradesh 4 Jhajjar Kangra Jammu Kathua Rajouri Sahebganj Sahebganj Raichur Raichur Raichur Yadgir Betul Burhanpur Chhindwara Dhar Khandwa Mandsaur Neemuch Umaria Gajapati Faridkot Gurdaspur Hoshiapur Sangrur Tarn Taran Ropar Amritsar Tarn Taran Amritsar Ganga Nagar Cuddalore Dindigul Nagapattinam Perambalur Ramanathapuram Tirunelveli Tiruvallur Tuticorin Nalgonda Azamgarh Badaun Bahraich Basti 0.36 0.03 0.03-0.05 0.03 0.03 0.01-0.03 0.068 0.01-0.04 0.063 0.051 0.01-0.04 0.01-0.05 0.01-0.03 0.01-0.05 0.03 0.01 0.01 0.01 0.01 0.01 0.01 0.02-0.03 0.01 0.02 0.02 0.07 0.055 0.2 0.06 0.04 0.02 0.04 0.01-0.02 0.02 0.01 0.01 0.01 0.01 0.01-0.02 0.01-0.04 0.03 0.01 0.02 Deoria Gorakhpur Jhansi Kausambi Kushinagar Maunath Bhanjan Pilibhit Shahjahanpur Azamgarh Maunath Bhanjan Deoria Lakhimpur Bahraich 5 0.01-0.03 0.01-0.04 0.02 0.02 0.01-0.03 0.05 0.01 0.01-0.02 0.054-0.811 0.061-0.082 0.051-0.083 0.051-0.086 0.054 Fig.1. Map showing arsenic concentration in India Table 2. Range of fluoride in groundwater in different parts of the India (Kabir et al., 2020). Andhra Pradesh State 6 Location Fluoride Level (mg L-1) Lower Vamsdhara River Basin ˃3-5 Anantapur District ˃5-10 Sarada River basin ˃1.5-3 Varaha River Basin ˃1.5-3 Talupula ˃5-10 Assam Bihar Chhattisgarh Delhi Gujarat 7 Gummanampadu Sub-basin ˃3-5 Coastal region between Chirala and Ongole ˃1.5-3 Anantapur Chittoor Guntur Hyderabad Krishna Kurnool Mahbubnagar Prakasam Nalgonda Guwahati Kamrup Diphu Goalpara Brahmaputra flood plains Karbianglong Rohtas Gaya Sabour Raigarh Durg Rajnandgaon Bastar Ambikapur Balrampur Kanker Korba Surajpur Dantewada Delhi National Capital Territory of Delhi Roop Nagar Najafgarh Ahmadabad Mehsana and Banaskantha Mehsana Kadi ˃5-10 ˃3-5 ˃ 10 ˃5-10 ˃5-10 ˃1.5-3 ˃1.5-3 ˃5-10 ˃5-10 ≥5-10 ˃ 10 ≤1.5 ≥3-5 ≤1.5 ˃ 10 ˃1.5-3 ˃ 10 ≤1.5 ˃5-10 ˃ 10 ˃ 10 ˃5-10 ˃5-10 ˃3-5 ˃1.5-3 ˃3-5 ˃ 10 ˃1.5-3 ˃3-5 ˃ 10 ˃5-10 ˃ 10 ≤1.5 ˃5-10 ˃5-10 ˃1.5-3 Haryana Jamm u & Jharkh Kash and mir 8 Amreli Anand Banaskantha Bharuch Bhavnagar Dohad Kachchh Narmada Panchmahals Patan Rajkot Sabarkantha Surat Surendranagar Vadodara Jind Hisar Pataudi Haily Mandi Harsaru Motipura Sirsa Sainiwas Faridabad Gurgaon Jhajjar Kaithal Kurushetra ˃5-10 ˃3-5 ˃5-10 ˃3-5 ˃3-5 ˃5-10 ˃3-5 ˃5-10 ˃5-10 ˃ 10 ˃1.5-3 ≤1.5 ˃1.5-3 ˃3-5 ˃3-5 ˃5-10 ˃ 10 ˃1.5-3 ˃5-10 ˃1.5-3 ˃ 10 ˃1.5-3 ˃ 10 ˃1.5-3 ˃1.5-3 ˃5-10 ˃5-10 ˃5-10 Mahendragarh ˃5-10 Panipat Rewari ˃5-10 ˃5-10 Rohtak ˃1.5-3 Sonepat Siwani ˃5-10 ˃ 10 Damodar River basin ˃3-5 Chukru Bishnah Doda ˃ 10 ≤1.5 ˃3-5 Karnataka Kerala Rajauri Kargil Gulbarga Raichur Bellary Kolar Tumkur and Chitradurga Kheru Ilkal Tamkur Shivani watershed area Bangalore Markandeya River basin Bijapur Chamarajanagar Chitradurga Davangere Gadag Farhatabad Tumkur Palghat Palakkad ˃ 10 ˃1.5-3 ˃5-10 ˃5-10 ˃5-10 ˃3-5 ˃3-5 ˃ 10 ˃5-10 ˃5-10 ˃1.5-3 ˃ 10 ˃1.5-3 ˃1.5-3 ˃1.5-3 ˃1.5-3 ˃1.5-3 ˃ 10 ˃5-10 ˃3-5 ˃5-10 ˃1.5-3 Malappuram ˃ 10 Kozhikode ˃ 10 Pathanamthitta ˃5-10 Wayanad Thrissur ˃ 10 Maharashtra ˃ 10 9 Amravati ˃5-10 Chandrapur Dhule Gadchiroli Gondia Nagpur Nanded ˃5-10 ˃1.5-3 ˃1.5-3 ˃1.5-3 ˃5-10 ˃3-5 Madhya Pradesh Manip ur Orissa Punjab Rajasthan 10 Gad River Basin ˃3-5 Yavatmal district ˃ 10 Chandidongri Chhatarpur Chhatarpur Chhindwara Dhar Guna Gwalior Jabalpur Jhabua Khargaon Shivpuri Imphal Thoubal Nayagarh boden Karlakot Angul Balasore Bargarh Cuttack Patiala Muktsar Amritsar Bhatinda Faridkot Fatehgarh Sahib Gurdaspur Moga Ghanaur Sangrur Pushkar valley Ajmer Hanumangarh Bhilwara Nagaur Pokhran ˃3-5 ˃1.5-3 ˃1.5-3 ˃ 10 ˃ 10 ˃ 10 ˃3-5 ˃5-10 ˃5-10 ˃5-10 ˃3-5 ˃1.5-3 ≤1.5 ˃ 10 ˃5-10 ˃3-5 ˃1.5-3 ˃5-10 ˃5-10 ˃1.5-3 ≤1.5 ˃1.5-3 ˃3-5 ˃1.5-3 ˃3-5 ˃ 10 ˃1.5-3 ˃1.5-3 ˃5-10 ˃3-5 ˃ 10 ˃3-5 ˃3-5 ˃ 10 ˃5-10 ˃3-5 Tamil Nadu 11 Alwar Banaswara Barmer Bhilwara Bundi Churu Dausa Dungarpur Ganganagar Jaipur Jaisalmer Jalor Jhunjhunun Jodhpur Karauli Kota Nagaur Pali Rajsamand Sirohi Sikar Sawai Madhopur ˃3-5 ˃3-5 ˃3-5 ˃5-10 ˃3-5 ˃ 10 ˃3-5 ˃3-5 ˃ 10 ˃5-10 ˃3-5 ˃5-10 ˃5-10 ˃ 10 ˃3-5 ˃3-5 ˃ 10 ˃5-10 ˃5-10 ˃3-5 ˃5-10 ˃3-5 Salem and Namakkal ˃ 10 Chennai Neyveli Tirupur Dindigul Erode ˃1.5-3 ˃ 10 ˃1.5-3 ˃3-5 ˃5-10 Thirumanimuttar sub-basin ˃3-5 Kancheepuram ˃3-5 Manur Mettur Thoothukudi Krishnagiri Madurai Dharmapuri Pambar River basin Perambalur ˃3-5 ˃3-5 ˃3-5 ˃5-10 ˃1.5-3 ˃5-10 ˃3-5 ≤1.5 Telangana Uttar Pradesh West Uttara Bengal khand 12 Puddukotai Ramanathapuram Tondiar river basin Vellore Siddipet Basara Nalgonda Vaniyar River basin Ranga Reddy Ranga Reddy (South Eastern part) ≤1.5 ˃1.5-3 ≤1.5 ˃1.5-3 ˃1.5-3 ˃3-5 ˃ 10 ˃5-10 ˃3-5 ˃3-5 Maheshwaram ˃3-5 Kurmapalli watershed Wailapally watershed Adilabad Medak Karimnagar Khammam Agra Saidabad Mat Kanpur Unnao Varuna River Basin Sonbhadra Marks Nagar Upper Panda River basin Bundelkhand Aligarh Etah Firozabad Rae Bareli Mathura Janghai ˃ 10 ˃5-10 ˃3-5 ˃5-10 ˃1.5-3 ˃1.5-3 ˃ 10 ˃1.5-3 ˃1.5-3 ˃5-10 ˃ 10 ˃1.5-3 ˃5-10 ˃ 10 ˃5-10 ˃3-5 ˃1.5-3 ˃1.5-3 ≤1.5 ˃3-5 ˃3-5 ˃1.5-3 Nainital ≤1.5 Nalhati Hooghly Bankura ˃1.5-3 ≤1.5 ˃ 10 13 Rampurhat ˃ 10 Junidpur and Nowapara ˃ 10 Haringhata Palta Rondiha Midnapore Town Hijli La0manpur Purulia ≤1.5 ˃1.5-3 ˃1.5-3 ≤1.5 ≤1.5 ≤1.5 ˃ 10 Fig. 2. Map showing fluoride concentration in different district of Indian States (Kabir et al., 2020) Table 3. Range of Iron in Groundwater in Different States of India. 14 State/UT Iron Contamination( above 1 mg/l) Andhra Pradesh Arunachal Pradesh Assam Bihar Chhattisgarh Gujarat Haryana Jammu & Kashmir Jharkhand 3 4 18 19 4 6 17 6 6 Karnataka Kerela Madhya Pradesh Maharashtra Manipur Meghalaya Nagaland Odisha Punjab Rajasthan Tamil Nadu Telengana Tripura Uttar Pradesh West Bengal Andaman & Nicobar 22 15 42 20 1 3 1 21 9 33 2 8 4 15 15 1 Fig. 3. Iron concentration in different states of India(Study on Groundwater Contamination, 2018) 15 2. Objective: To find out the best possible approach for the removal of iron, arsenic & fluoride from groundwater, focusing on rural areas. Maintenance & surveillance of Arsenic, Iron, and Fluoride Removal Plants. 3. Removal Techniques of Arsenic, Fluoride & Iron from Groundwater The following are the number of techniques for the removal of arsenic, iron & fluoride from ground water.(Jha & Tripathi, 2021) 3.1. Membrane Technology A system of integrated membrane hybrid treatment which removes arsenic from groundwater. Composite flat sheet(composed of polyamide in a cross-flow membrane module by pre-oxidizing all As(III) to As(V)) membranes are responsible for the successful purification of arseniccontaminated groundwater (Jha & Tripathi, 2021). Membranes are the synthetic materials with millions of pores that act as a selective barrier which does not allow any kind of impurities or harmful micro-organisms to pass through them. This technology is the most efficient techniques due to its advantages like easy operation, high arsenate removal efficiency, no sludge production. However, there are some limitations as well, like Membrane fouling, flux reduction and little expansive. (Worou et al., 2021). The process is classified into various types: Reverse osmosis (RO), Nano-filtration (NF), Ultrafiltration (UF), microfiltration (MF) and membrane distillation (MD) (Worou et al., 2021). 16 Fig. 4. Membrane Technology showing Reverse Osmosis, Nano Filtration, Micro Filtration & Ultra Filtration. 3.1.1. Removal by Reverse Osmosis (RO) Natural osmosis is a spontaneous phenomenon, which uses a semi-permeable membrane to permeate water molecule from low solute concentration to high solute concentration. In (RO), the osmosis process is reversed by pressure, thereby passing water molecules from higher solute concentrations toward lower solute concentrations (Hou, 2017).Reverse osmosis is the simplest, oldest and best available technology used in small water treatment systems to remove arsenic from water (Dutta et al., 2012). It is energy intensive and its operational cost is higher(Siddique et al., 2020). Principle: When two compartments containing solutions of different concentrations are separated by a semi-permeable membrane and hydrostatic pressure greater than osmotic pressure is applied on concentrated side the solvent moves from higher concentration to lower concentration side. 17 Fig. 5. Principle of Reverse Osmosis 3.1.2. Removal by Nanofiltration (NF) Principle: NF is a highly efficient, low-energy pressure-driven separation membrane technology for effective removal of low molecular weight solutes, such as salts, lactose, glucose, micropollutants, and natural organic matter in contaminated water. NF membranes are usually applied to separate multivalent ions from monovalent ions and successfully removes arsenate from contaminated water(Siddique et al., 2020). 18 Fig. 6. Principle of Nano-Filtration Nanofiltration membranes (NFMs) have emerged as a promising technique for high-quality drinking water production and wastewater treatment(Worou et al., 2021).Nanofiltration is nowadays preferred over reverse osmosis due to a more dilute concentrate waste stream, and the permeate water generated requires less stabilization in order to minimize distribution system corrosion. 3.1.3. Removal by Ultrafiltration (UF) Principle: Ultrafiltration (UF) is primarily a size exclusion-based pressure-driven membrane separation process. It leads to a separation through a semi-permeable membrane. Suspended solids and solutes of high molecular weight are retained in the retentate, while water and low molecular weight solutes pass through the membrane in the permeate. UF membranes typically have pore sizes in the range from 10 to 10000 A(Dutta et al., 2012). Water is passed through membrane surface (M) at a particular speed. The permeate is able to pass through the membrane (M) and the larger particles are left behind in a concentrated flow (the retentate). The hardened layer in this set-up is continuously removed by the cross-flowing supply flow(Ultrafiltration | EMIS, 2010). 19 Fig. 7. Principle of Ultra-Filtration Ultrafiltration (UF) is a membrane separation technology that separates, purifies, and concentrates solutions between microfiltration and Nanofiltration(Li et al., 2018). The process may not be useful for the removal of arsenic due to the large pore size of the membrane(Dutta et al., 2012). In the treatment of drinking water sources, only ultrafiltration technology is not very effective but when combined with other processes can show good performance. 3.1.4. Arsenic removal using Microfiltration (MF) Microfiltration is a low pressure membrane process which removes the contaminants mainly in the form of suspended solids and colloids. in the range 0.1 to 10 µm(Dutta et al., 2012). Usually ferric chloride is added in the water containing Arsenic. Ferric chloride hydrolyses and precipitates as ferric hydroxide, which is filtered out. It has been observed that successful reduction of As content is limited upto 2 μg/L (Singh et al., 2021). The process is usually utilized in conjunction with other conventional or membrane based treatments. 20 Fig. 8. Principle of Micro-Filtration 3.1.5. Arsenic removal using Membrane Distillation(MD)- Membrane distillation (MD) is a promising technology of the water-energy nexus suitable for generating high-quality water(Costa et al., 2021). Membrane distillation is a non-isothermal membrane separation process which employs a microporous hydrophobic membrane with pore size ranging from 0.01 µm to 1 µm(Dutta et al., 2012). In the membrane distillation process, a hot aqueous feed solution is brought in contact with one side of a hydrophobic, microporous membrane. After the evaporation of volatile molecules, to be separated from the feed, at the hot feed side, transport of vapor through dry pores of hydrophobic membranes occurs due to a vapor pressure difference across the membrane, which is the driving force (also known as trans-membrane vapor pressure difference) to drive the flux. 21 Fig. 9. Principle of Membrane Distillation. 3.2. Adsorption process Adsorption is the most extended technique for Arsenic, iron or fluoride removal due to ease of operation and low cost. As(V) can be easily removed by adsorption onto iron-based adsorbents, whereas As(III) is harder to remove (Garcia-Costa et al., 2021). The method is simple, costeffective, and efficient with minimum waste production and can be applied in water containing a trace amount of pollutants. Moringa oleifera is an effective and alternative biomass for removing As(V) from aqueous solution due to high bio-sorption capacity, easy availability, and being environmentally friendly (Sumathi & Alagumuthu, 2014). 22 Fig. 10. Principle of Adsorption process. 3.3. Coagulation –flocculation The term coagulation refers to the series of chemical and mechanical operations by which coagulants are applied and made effective.These operations are comprised of two distinct phases: Firstly, rapid mixing to disperse coagulant chemicals by violent agitation into the water being treated, and secondly, flocculation to agglomerate small particles into well-defined floc by gentle agitation for a much longer time. One of the following coagulants is used Alum -aluminium sulphate, Sodium aluminate, Ferric sulfate, Ferrous sulfate, Ferric chloride, Polymers. Flocculation follows coagulation in the conventional water treatment process. Flocculation is the physical process of slowly mixing the coagulated water to increase the probability of particle collision.The goal of flocculation is to form a uniform, feather-like material similar to snowflakes — a dense, tenacious floc that entraps the fine, suspended, and colloidal particles and carries them down rapidly in the settling basin. (Coagulation-Flocculation, n.d.). 23 Fig. 11. Principle of Coagulation-Flocculation. 3.4. Ion Exchange Principle: Ion-exchange method is a treatment process of removal of undesirable ionic contaminants from water by exchange with another non-objectionable or less objectionable ionic substance. 24 Fig. 12. Principle of Ion Exchange. Water that contains calcium and magnesium ions is also known as hard water. An unpleasant taste and odor occurs due to hardness of water which is unhealthy to drink. Ion exchangers can be effectively used to remove the hardness from water without raising the pH. Water softening removes divalent ions such as Ca++ or Mg++ from water. These ions are replaced by Na++. In dealkalization carbonate, bicarbonate, which contributes to alkalinity are removed and replaced with chloride ions. Similarly in demineralization, all cations are replaced by hydrogen ions (H+) and all anions are replaced by hydroxide ions (OH-) (Storrow, 1984). 3.5. Electro-Coagulation (EC) Principle: Electro-coagulation is a process of destabilizing suspended, emulsified or dissolved contaminants in an aqueous medium by introducing electrical current into the medium. The electrical current provides the electromotive force causing the chemical reactions. The process utilizes an anode and a cathode. Coagulant release is releases by electrolytically dissolving an electrode (anode, normally Fe or Al). O2 and H2 is released which results in 25 flotation effect (Elektrocoagulation | EMIS, n.d.). The following reaction electrolytic reactions occur in water At Cathode: (Reduction) 2H (aq) + 2e- H2(g) or 2H2O (l) + 2e- H2(l) + 2OH-(aq) At Anode: (Oxidation) 2H2O (l) O2(g) + 4H+ (aq) + 4eor 4OH-(aq) 2H2(g) + O2(g) Fig. 13. Principle of Electro Coagulation. 3.6. Oxidation process Oxidation involves the conversion of soluble arsenite to arsenate. However Oxidation alone does not remove arsenic from the solution, thus, a removal technique, such as adsorption, coagulation, or ion exchange, must be combined with oxidation for better result. For anoxic groundwater, oxidation is an important step since arsenite is theprevalent form of arsenic at near neutral pH . Aside from atmospheric oxygen, many chemicals, as well as bacteria, have already been used to directly oxidize arsenite in water. It has been found that atmospheric oxygen, hypochlorite, and permanganate are the 26 most commonly used oxidants. Generally oxidation of arsenite with oxygen is a very slow process, which can take hours or weeks to complete (Nicomel et al., 2015). 3.7. Nalgonda method. The first community de-fluoridation plant for removal of fluoride from drinking water was constructed in Nalgonda district, in the town of Kadri, Andhra Pradesh (Bose et al., 2018). Nalgonda Technique involves the addition of Aluminium salts, lime, and bleaching powder followed by rapid mixing, flocculation, sedimentation, filtration, and disinfection. Aluminium salt may be added as aluminum sulfate (alum) or aluminum chloride or combination of these two. It is responsible for removal of fluoride from water (Bose et al., 2018). During operation and maintenance of the de-fluoridation plant, physico-chemical parameters such as turbidity, conductivity, dissolved solids, pH, alkalinity, hardness, chloride, sulphate and fluoride are analyzed at regular intervals (Pal & Manna, 2010) 4. Field Based Applications 4.1. Arsenic Removal Plants in West Bengal. Principle: Tube-well attached arsenic removal plant consists of a gravel filter followed by an adsorption tower filled with granular ferric hydroxide. The raw water enters the first filter at the top and flows down the gravel bed to be freed from suspended particles in groundwater. The water exits at the bottom of the gravel filter and enters the adsorption tower at the top, where it flows down-ward through the AdsorpAs bed to be freed from arsenic concentration for potable use. The gravel filter and AdsorpAs of the ARP needs regular backwashing. The frequency of back-washing depends on both quality and quantity of the water treated. In order to backwash the gravel bed and AdsorpAs, tube-well water is pumped through the filter bed by closing the normal operation valves and opening the backwash valves. The backwashed water from the gravel filter and AdsorpAs, containing arsenic and iron, is discharged into a bucket. 27 Fig. 14. Handpump Attached Arsenic Removal Plant, West Bengal Flow rate of water Working pressure Media 12-15 Liter/min 2000 mm wc Granular Ferric hydroxide Based on this principle there were 1900 Arsenic removal plant installed in 5 Arsenic affected districts in West Bengal. 577 ARPs were investigated. Performance data was collected and analysed for 305 ARPs. 45 (25.1%) were found in non-working condition. Both raw and filtered water from 305 ARPs were analysed for total arsenic concentration. Among the 264 ARPs having raw water arsenic above 50 µg/L, 140 (53.1%) and 73 (27.7%) failed to remove arsenic below the WHO guideline value (10 µg/L) and Indian standard (50 µg/L), respectively (Hossain et al., 2006). 4.1.1. Maintenance: Backwashing: Only 131 ARPs undergo regular backwashing but 10 (out of 131) wash twice a week. The back washings from 80% of the ARPs were disposed on the open field. Limitation: Clogging occurs due to occurrence of sand in water and choking the tube-well and the filter media of ARPs. 28 Each ARP has a fixed media life. When the media gets exhausted it needs to be changed for consistent performance. It was often observed that many ARPs required changing their media (as mentioned by their respective manufacturers) well before adsorptive capacity due to clogging (Hossain et al., 2006) 4.2. Arsenic-Iron Removal Plant in Bangladesh The AIRP technology is based on consecutive processes: initial aeration and oxidation of iron and arsenic, then transformation into insoluble compounds, after that precipitation and finally two stage filters that reduce the concentrations by adsorption and filtration. The system can filter up to 1,200 litres of water per day. Each unit is designed for up to 35 households, although water volumes may vary. Working Principle: Ground water is extracted by a hand pump and travels through an aeration tray before settling in a sedimentation chamber. The water is pushed up through a filter of course gravels and shifted to a second chamber where it passes through filters of fine gravel. In the 3rd chamber, water is pressured down through a fine sand filter and a layer of charcoal before being pushed up into the storage unit. 29 Fig. 15. Hand pump Attached Arsenic Removal Plant, Bangladesh 4.2.1 Maintenance: Large maintenance of the system is performed by local operators and the main activity is to replace the filtering media every year, including the coarse and fine gravel and charcoal. The caretaker backwashes the filters weekly if iron concentration is very high. The dedicated cleaning group cleans the plant every 1–1.5 months and washes the filter media every 6 months, while more extensive maintenance includes the replacement of filter media yearly (Greggio, 2000). 30 Fig. 16. ARP in Bangladesh 4.3. Fluoride Iron Treatment Plant, Bihar- A Report by PHED Capacity of Plant: 40000 liters /day to feed the population of 1000. Bore well Discharge: 5100-6000 liters/Hr. Per Capita per day Supply of Water: 40 liters .Operation Time of Plant /day - 8 Hours . Capacity of Overhead Tank: 5000 liters. Fig. 15. Fluoride Removal Plant in Bihar by PHED 31 The system also includes 8 nos. of Stand Posts located at strategic points of the villages. The water being supplied from the overhead tank constructed on the roof of the treatment plant building. Raw water is been sent to sequence of components:- Solar Pump Oxidation Chamber Iron Removal Filter Alum Dosing System Fluoride Removal Filter Over Head Tank Distribution System Potable water at standpost for villagers Principle: Raw water is pumped by Solar Pump, then it is send to oxidation chamber for oxidizing & removal of Iron from raw water. The system provides for auto backwash of the filter bed. No regular maintenance required only media needs to be replaced once in a year Then water is passed to Iron Removal Filter. The vessel is filled with gravel, course sand and green sand (natural mineral) for further oxidation of residual iron and also filtration of water to make it free from precipitated and deposited iron on filter bed. The media needs to be replaced once in a year. The Iron Removal Filter (IRF) and the Fluoride Removal Filter (FRF) are equipped with a Multiport Filter Valve (MPV-Filter type) and a Multiport Softener Valve (MPV Softener type) respectively. The Multiport Valve (MPV) controls the flow of water through the granular media of a filter. The handle on top of the MPV can be set at any of the slotted positions to select the necessary function of the valve. Next in the Alum dosing unit, pH correction is done for adjustment of pH of water to the range of 5.5 to 6.5 to suit filtering media in FRF/ARF. It operates automatically and hydraulically for direct dosing of saturated alum solution. No regular maintenance required other than replenishing of chemical once it gets consumed. In the Fluoride Removal Filter- The vessel is filled with gravel, course sand and Activated Alumina Grade AAFS50. It works on adsorption principle. Spent material has met the Toxicity characteristic leaching procedure U.S.A (TCLP) and California Waste Extraction 32 Test (WET) Test. Media Life 15/ 18 Months( expected ) depending on the concentration of Fluoride in raw water. Backwash of media is performed once a month. Distribution Network comprises of GI pipes of diameters ranging between 65mm to 20mm, covering an approximate total length of 1000 m conforming to relevant standard and specification in trenches. The system also includes 8 nos. of Stand Posts located at strategic points of the villages. The water being supplied from the overhead tank constructed on the roof of the treatment plant building (Arvind Kumar Pandey.Pdf, 2015). Fig. 17. Installation of Fluoride- Iron Removal Plant in the villages of Bihar. 4.4. Well-head arsenic removal plants in remote villages of Indian subcontinent. Since 1997, more than 135 well-head arsenic removal units have been installed in remote villages in the Indian state of West Bengal bordering Bangladesh. Each unit serves approximately 200–300 households. Units contain about 100L of activated alumina. The arsenic concentration varies from 100 mg/L to more than 500 mg/L. Arsenic concentration in the treated water is consistently below 50 mg/L. The entire operation is manual and simple and does not require any electricity. The unit does not warrant any 33 chemical addition or sophisticated control. All one needs to do are open a valve, operate the hand pump and then collect essentially arsenic free water in a container. The upper chamber or head space of the column contains a splash distributor and atmospheric vent connections. This chamber ensures oxidation of dissolved iron into insoluble hydrated Fe(III) oxides or HFO(Hydrated Fe(III) Oxide) particles. Underneath the head space is the fixed-bed activated alumina followed by graded gravels and the treated water collection chamber. The design flow rate of the column operating under gravity is 8–10 L/min. The column is routinely back washed for 10–15 min daily and the backwash water is passed through a coarse sand filter to retain the HFO particulates. Fig. 18. a) Model of ARP attached with Hand pump (b)Installed ARP in the village of West Bengal 4.4.1 Maintenance: Each unit in every village is run, maintained and monitored through a committee appointed by the villagers. Arsenic present in the spent regenerant is transformed into a low-volume sludge containing 34 primarily ferric and aluminum hydroxide. The sludge is retained on the top of the coarse sand filter located in the same premise and no external disposal of sludge is necessary. Every regeneration produces a sludge weighing less than 400 g on dry basis (Sarkar et al., 2005) . 5. HOUSEHOLD APPLICATIONS: 5.1. Three-Gagri System in Nepal: This system is a variation of the Three-Kalshi System, a traditional water purification method used in Bangladesh and adapted there for arsenic removal. The Three-Gagri System works with the combination of the the processes i.e oxidation, precipitation, adsorption, and filtration. In the Three-Gagri System, arsenic is removed from influent water by iron species via precipitation and adsorption. The precipitate or sorbed solid is then filtered out of the effluent water. The system takes advantage of these processes by incorporating iron filings and sand into its design. Fig. 19. Model of Three Gagri System The arsenic in the water poured into the system will be removed by iron species. The iron filings in the top gagri provides these iron species. Since the system is aerobic i.e. oxygen is present, hydroxide species form on the metallic iron. The coarse sand, and later the fine 35 sand, acted as a filter to prevent the precipitate from flowing through the middle gagri, which allowed clean water to flow into the bottom gagri. In Nepal, nine batches of arsenic-contaminated water from one well were run through the three-gagri system. It lowers the effluent arsenic concentration to 9 ppb (Murcott, 2002). The results gave an average removal rate of over 98%. The daily capacity of the Three-Gagri System varies between 42 and 148 Litres/day or 1.75- 6.2 Litres/hour (Hurd, 2001). 5.1.1. Drawback: 1) The drawback of this system is the difficulty in disposing of the spent sand and iron as they become hazardous wastes (Murcott, 2002). 2) The system clogs easily. Clogging can significantly slow the flow rate (Hurd, 2001) . 5.1.2. Recommendations : 1) It has been suggested that wood charcoal can be added to the middle gagri for the removal organic impurities, but wood charcoal was not found in Parasi so it was left out of the design. 2) The user could then try and create more flow by poking holes in the cloth at the bottom of the gagri with a needle or develop new strategies to increase the flowrate (Hurd, 2001). 5.1.3. Maintenance: 1) Simple initial set-up and low maintenance. 2) The general practice with cleaning the gagri is to wash it in the morning and evening, and to rinse it out with each use. 3) When the gagri is cleaned, in 17% of the cases it is scrubbed with ash, 6% with dirt, 22% with soap, 19% with some combination (Collingwood & Paynter, 2001). 5.2. Hand Pump Attached Arsenic Removal Plant, Nadia District of West Bengal. Arsenic removal plants are generally attached to the existing hand pump tube wells, yielding arsenic beyond permissible level and generally they cater to the drinking water for the need of school, madras, health-center etc. The technology is again based on nano adsorbent, developed by IIT, Chennai. The hand pump is used by school students & local community, approx. 200 person. Iron removal is based on oxidation by resins (ISR) & 36 green sand and other filter media. Arsenic removal is based on nanoscale iron oxyhydroxide absorbent technology by IIT Madras. Fig. 20. Arsenic Removal Plant by IIT Madras 5.2.1. Operation: It is quite easy as with every stroke it delivers clean drinking water free of iron and arsenic through its lift & force option. It has option of drawing water for other purpose such as washing, bathing by using the normal mode of the hand pump. 5.2.2. Maintenance: By turning of few valves the system can be backwashed for few minutes and the system is recouped back for normal use. After each back wash the system is rinsed before drawing of clean water. This periodic cleaning/backwash depends on turbidity level/iron content in the input water. The Arsenic Absorbent Unit doesn’t require any backwash as it simply needs to replace with new cartridge after the same is exhausted (Report on Field Visit of Joint Secretary ( Water ) to Nadia District of West Bengal to Review Arsenic Mitigation Measures – 11th and 12th September , 2015, ). Total 330 such Units have been installed in the schools and some habitations, in the district of Nadia, Murshidabad. 37 5.2.3. MODEL 2: There is another model of handpump: Location of the handpump is Sealmara Madhyamik Siksha Kendra - Berhampore Block – District Murshidabad. Design is Coconut shaped which attracts people and especially the children. This handpump is used by school students & local community, approx 250 people. Iron removal is based on Terafil Filters. Arsenic removal is based on nanoscale iron oxyhydroxide absorbent technology by IIT Madras. Output is 1200 liter per day. Fig. 20. Arsenic Removal Plant by IIT Madras 5.2.4. Operation: Easy to operate the system works on gravity flow principal. Only daily filling of water through a lift & force (it also has option of drawing water from other purpose such as washing, bathing) or through a electric mono block pump 5.2.5. Maintenance: The Upper Tank of the systems storing raw water requires periodic cleaning depending on turbidity level/iron content in the input water. The filtrates clog the top surface of the Terafil over time and hence flow rate drops. This requires cleaning/scrubbing the surface of the cake rigidity with a soft nylon brush / coir / or spay of water with the sprayer provided with the system. This will remove the sediments and open new pores for rejuvenation of filtration process. The Arsenic Absorbent media doesn’t require any maintenance, only it simply needs to replace with new cartridge after specific interval (Report on Field Visit of Joint 38 Secretary ( Water ) to Nadia District of West Bengal to Review Arsenic Mitigation Measures – 11th and 12th September , 2015, 2015). Total 1000 such units are being installed in Schools/ Anganwadis/ Madrasah/ Health Centres/ Mosque/ Habitation etc. in the district of Murshidabad, West Bengal. 5.3. Kanchan Arsenic Filters in the lowlands of Nepal Since their introduction in 2006, iron-assisted bio-sand filters (Kanchan filters) are widely used to treat well water in Nepal. The filters are constructed on the basis of Arsenic removal with corroding zero-valent iron (ZVI), with water flowing through a filter bed of iron nails placed above a sand filter (Mueller et al., 2021). KAF is an award winning and the most commonly used household water filter in Nepal developed by Massachusetts Institute of Technology (MIT) Civil and Environmental Engineering Department, in partnership with Environment and Public Health Organization (ENPHO) and Rural Water Supply and Sanitation Support Programme (RWSSSP), Nepal. Based on the principle of a bio-sand filter, it uses an innovative diffuser basin containing iron nails for removal of As. It simultaneously remove arsenic as well as pathogens. The filters were designed to remove pathogens by physical straining and by predation of pathogens in the lower sand layer, as well as to eliminate arsenic by sorption on Fe(II,III)(hydr)oxide phases produced from corrosion of ZVI in the form widely available iron nails, placed in a perforated bucket above the sand layer. First field tests results shows that Kanchan filters removed more than 95% arsenic on average (Mueller et al., 2021). It has been found that out of 62 tube wells, 41 had influent arsenic concentrations exceeding the Nepal drinking water quality standard value (50 lg/L). Out of the 41 tube wells having unsafe As levels, KAFs reduced arsenic concentrations to the safe levels for only 22 tube wells (Mueller et al., 2021). 5.3.1. Limitations: Corrosion occours during the short contact of the nails with water (Mueller et al., 2021). 39 5.3.2. Modifications: In order to increase the efficiency of the filter, Iron mesh in place of iron nails can be used to enhance arsenic removal efficiency of the filter. The study revealed that the removal efficiency for iron mesh (88%) was much higher than iron nails (50%) over a period of one week. The long-term efficiency for iron mesh (99.90%) was also greater than that for iron nails (98.94%) (Timalsina et al., 2021). Integration of a hair layer may increase overall performance of the KAF, particularly with respect to removing As and some heavy metals, and with minimal addition of cost. Integration of a hair layer may increase overall performance of the KAF, particularly with respect to removing arsenic and some heavy metals, and with low cost.Iron mesh gives the highest removal efficiency for As compared to iron slags and nails because of the higher relative surface area of the mesh material (Timalsina et al., 2021). When required on a large scale, As removal could be achieved using a hair layer integrated with the bio-sand multistage filter .The combination of a hair layer and iron mesh in a bio-sand filter improves the overall filter performance for community use (Timalsina et al., 2021). 40 Fig. 21. Kanchan Arsenic Filter, Nepal 5.3.3. Maintenance: The sorbent media (iron mesh and hair layer) should be cleaned regularly to expose more iron surface for rusting, and replaced periodically either on a set frequency or based on monitoring and tracking use. It is suggested that the sand should also be replaced annually in order to maintain sorption capacity (Timalsina et al., 2021). The iron mesh must be constantly wet, but should not be completely immersed inside water so as to promote rust formation for releasing higher Ferric oxides. Also, there should be sufficient contact time between the iron mesh and arsenic which can be achieved by preventing the formation of holes and dents in the iron mesh layer. Use of polyester cloth to separate the iron mesh layer and sand layer can facilitate for cleaning of filter. Also, the filter should not be exposed to direct sunlight for a longer duration as the increase in temperature is reported to reduce efficiency of the filter (Timalsina et al., 2021). 41 6. Filters developed by different institutes. 6.1. Laterite based Arsenic Filter by Indian Institute of Technology- Kharagpur: Laterite based arsenic filter is designed and fabricated for domestic and community scale. For domestic, single stage adsorption technology is used and double stage sedimentation followed by adsorption is used in Community level. Removal of arsenic, iron and bacteriological contamination is done in a single unit. Removal capacity of arsenic (total) is 32.5 mg/g. This is maximum among other Arsenic adsorbent materials such as expensive activated alumina, iron oxide coated sand, iron based commercial adsorbent etc. Raw, naturally abundant laterite (commonly known as MORAM) is modified using suitable chemical treatment (acid-alkali treatment). The filter removes Iron below permissible limit in drinking water (1 ppm) and more than 98% of pathogenic contaminants. No regeneration of adsorbent (filter medium) is required. Alum dosing is done (15 mg/l) to remove iron. The capacity of domestic filter is in the range of 40-120 litres/day and for community scale it is in the range of 500-2000 litres/day. These units are scalable as well. Flow rate for domestic filter is 4-5 lph and that for community is 100-2000 lph. Electricity is not required for Domestic but for community scale 1.5 kWh-30kWh required for operating the pump. 25 Household filter units and 3 community filter-based units have been installed in West Bengal till 2012. Maintenance: Maintenance is easy. Spent material meets TCLP (Toxicity Characteristic Leaching Procedure) protocol and can be safely disposed (“Department of Science & Technology,” 2015). 6.1.2. Drawbacks: 1-Disadvantages of the adsorption process is the periodic regeneration of adsorbent and monitoring of breakthrough of filter bed. 2- This treatment produces pollutants (Saadon et al., 2018). 42 Fig. 22. Domestic scale filter in the villages of West Bengal Fig. 23. Community scale filter of 500 litre /day installed in a primary school in Kashinathpur in Rajarhat, near Kolkata 6.2. Arsenic Filter by Indian Institute of Technology- Bombay IIT Bombay has developed a community scale hand pump attached arsenic removal filter using indigenous Zero-Valent Iron (ZVI) technology. The method is based on corrosion of ZVI and generation of hydrous ferric oxides (adsorbent for arsenic) and subsequent filtration. The process is designed in such a way that oxidation of As (III) to As (V) is achieved and also the As (V) formed is adsorbed on hydrous ferric oxide (HFO). Technology is based on Dual Stage-Gravel Filtration with iron nails and jali for 43 supplementing iron for arsenic removal. Removal process based on dissolution of iron to Fe2+ from ZVI (iron nails + Jali) and co-oxidation of Fe2+ and As3+ which is coprecipitated with Fe3+. The gravel media has very long life but reactive media (Iron nail + iron Jali) need to be supplemented in a year time. For sludge disposal, a brick masonry tank is being designed. 2 units operating at a flow rate of 600 lph in villages of West Bengal from February 2008. 53 more such units installed in various parts of Uttar Pradesh, Bihar, West Bengal and Assam. 3 units installed in 2010 at Polasi (N 24 Parganas), Kalyani Mor and Sonakhali (Nadia district) (“Department of Science & Technology,” 2015). Fig. 24. IIT B Arsenic removal units in West Bengal 6.3. AMRIT- Arsenic and Metal Removal by Indian Technology- Indian Institute of Technology- Madras. AMRIT is an affordable solution for providing clean drinking water in arsenic affected areas. It is a gravity-fed water purification unit in which arsenic and iron containing water is passed through a composite filter unit to obtain water. The technique has multiple stages; 1st stage: Surface Filtration, 2nd stage: Colloidal Iron adsorption, 44 3rd stage: Arsenic adsorption, 4th stage: Metal-based disinfection The technology is designed for domestic and community scale for the removal of Arsenic, iron and turbidity. The process of synthesis is simple. It is prepared in a manner as nature prepares seashells, materials are made at room temperature in water, yet the materials are stable in water. These aspects make the innovation scientifically unique, green and sustainable. The design is inspired from a coconut which is known to contain one of the finest forms of drinking water made by Mother Nature. Flowrate for domestic filter is 3lph & for community is 100-1000 lph (in case of gravity flow), up to 20,000 lph (in case of motor-powered flow) Reject Management: Media can be easily disposed in the landfill as it is prepared with facile and eco-friendly materials. Media can also be used for brick making as it is composed of iron oxides. 200 household units demonstrated in Yadgiri District of Karnataka, Murshidabad district of West Bengal and in Bihar 160 units of community filter demonstrated in villages spread across the districts of Murshidabad and Nadia, (West Bengal) (“Department of Science & Technology,” 2015). 45 Fig. 25. AMRIT, Domestic Arsenic Filter Fig. 26. AMRIT community water purification unit. 6.4. Arsiron Nilogon Arsenic Filter by Tezpur University. The filter is designed for domestic and community scale for removal of Arsenic and Iron. Technology is based on 2 stages: 1st stage: Oxidation-coagulation adsorptionsedimentation 2nd stage: Slow Sand Filtration. This filter removes arsenic and iron by Oxidation-Coagulation at Optimized pH (OCOP). Here the arsenic and the iron present in groundwater are oxidised from As(III) (arsenite) and Fe(II) (ferrous) states to As(V) (arsenate) and Fe(III) (ferric), respectively by using an oxidizing agent, viz., potassium permanganate (KMnO4) and then coagulated using a coagulant, viz. ferric chloride (FeCl3) at an optimized pH range controlled by adding sodium bicarbonate (baking soda or cooking soda, NaHCO3) before oxidation and coagulation. Aeration of the water reduces the required quantity of KMnO4.The water is then filtered using any filter, preferably a sand-gravel filter fitted with a filtration assisting device. Arsenic can be removed to/below 5 ppb (g/L) from up to 500 ppb of initial concentration. Similarly, iron can be removed to below 0.1 ppm (mg/L) from up to 20 ppm of initial concentration. The method is simple. Operation is also very simple, a plumber or a school teacher can be easily trained to operate or use it. 46 Flowrate of household filter is 200 lph and community filter is 500 lph.It can be scaled up with hundreds of litres for school and small community. It can also be scaled with lakhs of litres for large public water supply scheme. Reject Management: The small solid sludge produced can be disposed safely in the landfill. Very small amount of sludge collected and sludge shows very low leaching (<10 ppb). 25 Household filter units are installed so far in West Bengal. Totoya Gaon, Majuli, District Jorhat, Assam Installed in 2013 Sariyohtoli, Lakhanabondha, District Nagaon, Assam Installed in 2014 Dangdhara, Titabor, District Jorhat, Assam Installed in 2014. Tantigaon, Titabor, District Jorhat, Assam Installed in 2010 Community Filter: 1 (in PHED supply scheme) at Jyoti Nagar in Golaghat town of Golaghat district in Assam and in 6 Schools (“Department of Science & Technology,” 2015). Fig. 27. Community models for Arsiron Nilogon arrangements 47 Fig. 28. Household Arsiron Nilogon system with sandgravel filter alone (HAN) 6.5 DRDO Arsenic Removal Filter by Defence Research and Development Organisation. A domestic arsenic removal filter has been developed by Defence Research and Development Organization (DRDO). The filter is user friendly, economic, does not require electricity its operation. Maintenance is easy. The filter works on the principle of co-precipitation of arsenic with iron and adsorption of this precipitate on iron oxy-hydroxides which is followed by further retention of this precipitate in treated sand. Arsenic removal filter has been designed and fabricated in clay, plastic and in stainless steel. The filter was demonstrated and evaluated in the arsenic affected rural areas of West Bengal, UP & Bihar. It is used for domestic purpose and flow rate is 15lph. Reject Management: The absorption media is is converted in to non-leachable cement bricks after use (“Department of Science & Technology,” 2015). Fig. 29. 3 Types (Stainless Steel, Clay and Plastic) DRDO Water Filters. 48 Fig. 30. Reject Management by conversion of the waste into non leachable cement bricks. 6.6. ARI Groundwater Arsenic Treatment Plant by Agarkar Research Institute The filter removes odour, color or sloughed off cells from water. The treatment capacity of the filter is 1000 liters/ day which can be easily scalable upto 10000 liters/day. The filter is operated and maintained by skilled/unskilled workers. It is a multi- stage (assembled single integrated unit). 1st stage- Microbial oxidation (Bio-oxidation of As3+ to As5+ using a bacterium (Microbacterium Lacticum immobilized on brick pieces) 2nd stage- Adsorption of arsenate (As5+) on alumina. 3rd stage: Filtration using charcoal to remove odour, colour, microbial cells. 4th stage: Ultra Violet Radiation for disinfection. This filter is used as a community filter and its flow rate is 40lph. It requires electricity i.e 90 units per month. Reject management:- The washed water from the columns is collected in a separate container and 3% Ferric chloride is added to it to form an arsenic iron complex (indicated by the formation of a red precipitate). The resulting sludge is then disposed off in the concrete pit after drying. The system is demonstrated at 5 locations (Koudikasa and Muraithitola villages) in the state of Chhattisgarh (“Department of Science & Technology,” 2015). 49 Fig. 31. ARI groundwater Arsenic removal unit 6.7. Hand Pump Attached Arsenic Removal Unit by Jadavpur University The treatment process is based on the double principle of Oxidation & Co-precipitation and Adsorption. The oxidation of As (III) to As (V) is achieved by adding chlorine. Co-precipitation for removal of arsenate is achieved by adding alum (aluminum sulphate) in correct proportion. During up-flow movement of water, arsenate or arsenite, if present are removed through adsorption process in activated alumina layer. The filter removes Arsenic and Iron both. Features: 1- Present running capacity 4,800 L in 12 hours. 2- Per-capita supply (for drinking and cooking) 8 litre/d. 3- Arsenic concentration in raw water is 0.1667 mg/litre. 4- Arsenic concentration in treated water is 0.008 mg/litre. 5- Flowrate of the filter 800 lph to 1000 lph. 6- No electricity needed. Reject Management- Arsenic-rich sludge is stored in underground reservoir. Arsenic sludge (1%) needs to be mixed with concrete for reject disposal. 50 The system is demonstrated at 4 locations i.e. Lalgola block of Murshidabad in West Bengal (“Department of Science & Technology,” 2015) Fig. 32. Arsenic Removal Unit (ARU) Fig .33. Villagers collecting water from Arsenic Removal Unit (ARU) 7. Sludge Disposal Methods From the above case studies it is found that the general issue for most of the filters is sludge management. Regeneration of activated alumina and ion exchange resins results in various semi liquid wastes that may be acidic, caustic, saline, and too arsenic rich for simple disposal. Hence, environmentally safe disposal of sludge, saturated media, and liquid wastes rich in arsenic is a concern. 1-Disposal in on-site landfill/ sanitation pits . 2- Mixing with concrete in a controlled ratio. 3- Mixing with clay for burning for brick manufacturing. 7.1. Disposal in on-site sanitation pits/ landfill Groundwater constitutes 97% of all freshwater that is potentially available for human use. Groundwater is therefore of fundamental importance to human life. On-site sanitation systems 51 can lead to contamination of groundwater sources. The contamination takes place in the event of a pathway existing between a source i.e. on-site sanitation system and a receptor. 7.2. Mixing with concrete in a controlled ratio: Another commonly used treatment is cement based solidification and stabilization (s/s). Cement is used to treat a large range of hazardous wastes by improving physical characteristics and decreasing the toxicity and transmission of contaminants. This process involves mixing the waste, either in form of sludge, liquid or solid, into a cementitious binder system. 7.3. Mixing with clay for brick manufacturing: The physical property requirements in most specifications are water absorption capacity, Saturation coefficient, Specific gravity, Specific Surface Area (SSA), optimum moisture content (OMC), Toxicity Characteristics Leaching Procedure (TCLP) using USEPA Method 131. It was observed that, with increase in percentage of sludge the compressive strength of the bricks decreases with all firing temperatures (Mandal et al., 2016). 8. Conclusions Water is an indispensable natural resource for the survival and well-being of every individual. Consumption of safe and acceptable water is essential for every individual in this planet. The first and foremost consequence of lack of safe water for community consumption is diseases which caused due to ground water contamination. The most three harmful contaminants are Arsenic, Iron and Fluoride. Hence all the above mentioned techniques are required to remove these contaminants. It is a major concern for rural water supply as people in rural village doesn’t care about maintenance and monitoring of the system. Due to lack of sludge management, membrane fouling, improper monitoring etc. the system fails, which results in poor consumption of water. The above case studies helped us to understand the different removal techniques of Arsenic, Iron & Fluoride and their how they managed the sludge being produced. In the above studies we found some most general way of handling sludge like land disposal, mixing with concrete or clay etc. The real life examples helped us to know their condition, further it can be helpful for implementing the similar techniques in the rural areas which are arsenic, fluoride or iron contaminated areas. 52 From all the studies it has been found that Adsorption is the leading technology as it has been used by most of the PHED. Moreover in rural villages this method can be effective due to less expensive and simple handling. 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