UNIVERSITY OF NAIROBI
ENVIRONMENTAL & BIOSYSTEMS ENGINEERING
DESIGN OF A BIOLOGICAL SLAUGHTERHOUSE
WASTEWATER TREATMENT SYSTEM (USING AN ANAEROBIC
BAFFLE REACTOR – CONSTRUCTED WETLAND SYSTEM)
< CASE STUDY OF KISERIAN SLAUGHTERHOUSE>
Mwangi Simon Thuku
F21/2492/2009
Supervisors : Mr. Orodi Odhiambo
Eng. D. A. Mutuli
BACKGROUND
Approximated slaughterhouse waste content and NEMA standards
for disposal into the environment
Waste Content
Slaughterhouse
(approx.)
NEMA Disposal
Standards
BOD 5days at 20 oC
1000 – 4000 mg/L
30 mg/l
COD
2000 – 10000 mg/L
50 mg/l
Oil and grease
High
Nil
Total Suspended Solids 200 – 1500 mg/L
30 mg/l
Total Nitrogen
100mg/l
Johns et al., 1995; Manjunath et al., 2000, NEMA
BACKGROUND Cont’d
Treatment Options
 Anaerobic treatment + activated sludge
 Anaerobic treatment + contact aeration
 Activated sludge + chemical coagulation
 Contact aeration + chemical coagulation.
PROBLEM STATEMENT
• This waste water flows to R.
Kiserian and eventually gets to
Kiserian Dam.
• This causes eutrophication and
anoxia in the water bodies.
• Waste from slaughterhouses
also leads to air and soil
pollution
Pre- treated Wastewater getting into the streams
Parameter
pH
TSS, mg/l TDS, mg/l
COD, mg/l BOD5mg/l NH4+N (N)mg/l
Content
7.75
2315.25
3262.5
3070
936.25
141.5
Site Analysis
• Kiserian is a settlement in
Kajiado county
• Habitants are mainly
pastoralist community
• Warm and Temperate
climate.
• Rainfall =833mm
• Temperature = 17.8
OBJECTIVES
Overall objective
To design a biological slaughterhouse wastewater
treatment system
Specific Objectives
i.
To analyze the amount and the content of
wastewater
ii.
To establish pertinent parameters for design
of a biological slaughterhouse waste water
treatment system.
iii. To use the parameters from (ii) to size the
baffle reactor and the constructed wetland.
STATEMENT OF THE SCOPE
Survey work
 Carrying out tests
 Determination of System Design Parameters
 Making detailed engineering drawings

Literature review
Treatment Process ( primary, secondary and tertiary
treatment)
Why anaerobic?
Anaerobic Baffle reactor (improved septic tank)
Constructed Wetland
Methodology
Survey
Soil and waste
water sampling
Laboratory tests
(soil & waste
water)
Determining the
efficiency of
ABR
ABR volume
determination
Result analysis
Designing the
wetland
Structural
design of the
ABR
Theoretical Framework
Chemical oxygen demand,
Biochemical Oxygen Demand, BOD5,mg/L =
Design Criteria for an
Anaerobic baffle reactor
Hydraulic Retention time, HRT
>24 hours at maximum sludge
depth and scum accumulation
Sludge Accumulation Rate, SAR
Depending on TSS removal rate
and waste water flow
Sludge and Scum Accumulation
Volume
Sludge Accumulation Rate
multiplied by flow rate
Desludging interval
>1 year
Number of upflow chamber, N
>2
Maximum upflow velocity, v
1.4 – 2m/h
Sasse (1998), Wanasen (2003), Foxon et al., (2004) etc
Results
Parameter (ABR)m
Formula
Results
Flow rate, Q
(200 x C) + ( 100 x S)
14.5m3/day
Length of upflow chamber, Lc
=< half depth
1m
Maximum Peak Upflow Velocity,
Vp
Q/t
2.4167m3/h
Area of upflow chamber, Au
Vp/v
1.343m2
Width of the chamber, Cw
Cw/Lc
1.343m2
Actual upflow velocity, Va
Vp/(Lc x Cw)
1.208 m/h
Actual working volume, V
Cw x d x (Lc+ Ld)N
30 m3
Hydraulic Retention Time, HRT
V/Q
2 days
BOD removal
BODeff = BODin e- Kt x T 135.18 mg/l
Organic Loading Rate
(CODin x Q)/ V
≈2m
1.314 kg COD/m3.d
Results Cont’d
Parameter
Value
Results
BOD5 removal, percent
80 to 90%
93.625mg/l
COD removal , mass
1.6 x BOD5, removal
1348.2mg/l
Biogas production
0.5m3/kg COD removed
9.77 m3
Methane production
0.35m3/kg COD removed
6.84m3
Leslie C.P. et al, 1999
Results Cont’d
Parameter (CW)
Formulae
Water Budget
Qe = Qi + (P – ET) As
Surface Area of the system, As
As = (Qave(ln Co – ln Ce))/Kt x d x n
Aspect Ratio
between 2:1 to 3:1 (Mitsch et.al 2007)
Retention Time ,t
(Lwyn)/Q (Crites et.al, 2006)
Bed Slope
0.5% to 1%
Qi = 14.5m3/d
y = 0.7 m
As = 126.22 m2
t = 1.85 days
width = 7.94 m
dh = 0.01 x 15 = 0.15m
Length = 2 x 9 = 16 m
slope is taken to be 1.5
Drawings
Drawings
Drawings
Drawings
Drawings
Conclusion
• Objectives of the design project were met.
• slaughterhouse wastewater was observed to have high content of waste.
•The BOD5 removal efficiency for the ABR was found to be 90% (i.e. from
936.25mg/l to 93.625mg/l) with a HRT of 2.38days. The organic lading in the
ABR was found to be 1.314 kg COD/m3.d (should range between 1 – 3 kg
COD/m3.d).
•The CW reduced the concentration of nitrates in the waste water from 141.5
mg/l to 100 mg/l and the BOD from 93.625mg/l to 15.62mg/l.
•System was found to have a 98.4% BOD reduction
Recommendations
•The first compartment of the ABR should be modified and increased in size to
trap as much solids as possible.
•The ABR should be made air tight and a system to improve/increase the pressure
of the biogas in the reactor to allow gas collection otherwise the first compartment
can be constructed in such a way that it has a gas holder and made airtight (shape
of a fixed dome).
•A gradient should be created between the ABR and the CW so as to utilize gravity
as the driving force.
•Wastewater monitoring/ testing should be done on a regular basis in order to
ensure that the content of waste flowing to the stream conforms with the NEMA
standards and as a way of monitoring the performance of the system.
References
• Muench, E. (2008): Overview of anaerobic treatment options for sustainable
sanitation systems. In: BGR Symposium "Coupling Sustainable Sanitation and
Groundwater Protection".
• Bachmann, A., Beard, VL. and McCarty, PL. (1985). Performance
Characteristics of the Anaerobic Baffled Reactor. Water Research 19 (1): 99–
106.
• Sergio S. Domingos (2011), Thesis on Vertical flow constructed wetlands for the
treatment of inorganic industrial wastewater, Murdoch University WA, Australia.
• Morel A. and Diener S. (2006). Greywater Management in Low and MiddleIncome Countries, Review of diff erent treatment systems for households or
neighbourhoods. Swiss Federal Institute of Aquatic Science and Technology
(Eawag). Dubendorf, Switzerland.
• Nijaguna B.T. (2002), Biogas Technology, New Age International (P) Limited,
New Delhi.
References
• Rustige H &Platzer Chr. (2000),Nutrient Removal in Subsurface Flow
Constructed Wetlands for Application in sensitive Regions in: Proceedings – 7th
Int. Conf. On Wetland Systems for Water Pollution Control, Orlando, USA
•Leslie Grady .C, Glen .T, (1999), Biological Wastewater treatment, 2nd ed, Maral
Dekker ,Inc, New York
•Foxon KM, Pillay S, Lalbahadur T, Rodda N, Holder F, Buckley CA (2004) The
anaerobic baffled reactor(ABR): An appropriate technology for on-site sanitation.
Water South Africa 30, 44-50.
•Lawrence A.W. and McCarty p.L (1970): Unified basis for biological Treatment
Design and Operation. J. Sanit. Eng. Div., Am. Soc. CivEngrs.
•Walter R.H., Shermah R.M. and Downing D.L. (1974): Reduction in Oxygen
demand of abattoir effluent by Precipitation with metal. J. Agric. Fd Chem
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