Performance Evaluation of Solubilization System on Biological
Solubilization and Mineralization Processes for Food Waste Treatment
*1Hazel B. Gonzales, 1Takehiko Gondo, 2Hideki Sakashita, 2Yoichi Nakano,
2
Wataru Nishijima and 1Mitsumasa Okada
1
Department of Chemical Engineering, Graduate School of Engineering, Hiroshima
University, 1-4-1 Kagamiyama, Higashi-Hiroshima 739-8527 Japan
2
Institute for Wastewater Treatment, Hiroshima University, 1-5-3 Kagamiyama, HigashiHiroshima 739-8513 Japan
ABSTRACT
Biological solubilization and mineralization process was proposed for food
wastes. In the process food wastes are mixed with rice hull as biological support medium
under wet condition and are solubilized or mineralized. The purposes of the study are to
operate the biological solubilization and mineralization process without accumulation of
food wastes and to increase mineralization rate for the reduction of organic loading to the
sewerage system. Biological solubilization and mineralization process was operated
without the accumulation of food waste by aeration in the circulation tank. The process
can reduce organic loading to the sewage system to half by aeration in the circulation
tank and 80 % by installing biofilm into the circulation tank. The process combined with
biofilter would not require further treatment of effluent.
Keywords: Food waste; solubilization; mineralization; biological treatment
1. INTRODUCTION
At present, direct landfill and landfill after incineration are the most common
technologies being used to handle food wastes (Kreith, 1994; Shin et al., 2001).
Although food wastes contain more than 80% water aside from oil and biodegradable
organic matter (Yun et al., 2000), the incineration of food wastes requires large amount
of energy and direct landfill induces sanitary problems such as the production of flies and
other pathogenic microorganisms and putrid odors associated with anaerobic
decomposition. Some researchers mentioned that treating food wastes in a wastewater
treatment plant might be more effective due to the high water content (Wang et al., 2001;
Strutz, 1998; de Koning and van der Graaf, 1996). In some countries such as US,
Sweden and Australia, food wastes are treated by disposers or grinders in the site where
food wastes are produced before discharge to wastewater treatment plants to help the
degradation (Karrman et al., 2001; Gallil and Yaacov, 2001). However, the use of
disposers entails additional loading to sewerage systems (Sankai et al., 1997; Gallil and
Yaacov, 2001).
Biological solubilization and mineralization process was proposed for food wastes
(Okada and Nishijima, 2001). In the process, food wastes are mixed with rice hull as
biological support medium under wet condition and are solubilized or mineralized. The
process can reduce organic loading to the sewerage system due to mineralization. The
purposes of the study are to operate the biological solubilization and mineralization
process without accumulation of food wastes and to increase mineralization rate for the
reduction of organic loading to the sewerage system.
2. MATERIALS AND METHODS
2.1. Reactor Specification and Operation
The schematic diagram of the equipment is shown in Figure 1. A 25-L stainless
steel reactor was used as solubilization reactor and a 58-L polypropylene container was
used as circulation tank. The solubilization reactor was equipped with an impeller and a
stainless steel rod sprinkler for mixing and water addition, respectively. Rice hulls (15L)
were introduced in the solubilization reactor as support media for microorganisms.
Activated sludge (200 g-dry weight) and 130g activated carbon were also added at the
start of operation. The reactor has a stainless steel perforated plate (2mm pore-diameter)
at the bottom allowing the flow of water containing solubilized wastes to the circulation
tank while preventing the loss of solid wastes and support media. The circulation tank
was filled with water and a pump in the tank intakes surface water with oil and bottom
water with sedimentary particles and transfers back to the solubilization reactor. Effluent
was discharged as overflow water from the mid-depth of the circulation tank.
The equipment were operated with and without aeration in the circulation tank
(Run 1 and Run 2, respectively). To trap suspended solids (SS) and degrade dissolved
and suspended organic substances, coiled filters (polyvinylidene chloride) were installed
inside the circulation tank (Run 3). Twice as large as the amount of air in Run 2 was
supplied to the circulation tank in Run 3 for the degradation of dissolved and suspended
organic substances. Biofilter was also installed, instead of coiled filter, outside the
circulation tank for the same objectives (Run 4). The biofilter consisted of a series of 6
columns with expanded/foamed polypropylene as packing material and connected to the
circulation tank. Air was supplied to the circulation tank and biofilter. The total air
supplied in Run 4 was the same as Run 3.
water supply
food waste
circulating
water
sprinkler
solubilization
reactor
impeller
support media
weighing
scale
perforated
plate
effluent
circulation tank
Figure 1. Schematic diagram of the biological solubilization equipment
During the operation, 400 g/d of food wastes (food waste loading; 16.0 kg/m3/d)
were added once a day to the solubilization reactor. Water was also added to the
solubilization reactor once an hour at a feed rate of 1 l/h. Water in the circulation tank
was also transferred to the solubilization reactor once an hour. Water addition and
circulation are in 30-minute interval. The solubilization reactor was operated at 35ºC
while the circulation tank was at room temperature.
2.2. Food Wastes
Artificial food waste was used to keep its properties constant. The composition of
artificial food waste was determined based on a typical composition of food waste from
Japanese household (Aoshima et al., 2001) as listed in Table 1. The average moisture
content of the food waste was 82 % and contains 42 % carbon and 2 % nitrogen per dry
weight basis. The waste was chopped to 1-cm cube size and stored in a refrigerator at 4
ºC before use.
2.3. Sampling and Analyses
Solid sample was collected from the solubilization reactor and the weight of the
reactor was recorded prior to the daily feeding of food wastes. The solid sample was
subjected to moisture content (oven-drying at 105ºC for 24 hours), carbon and nitrogen
(Yanaco MT-CN Corder, Japan) analyses. The effluent from the circulation tank was
also sampled and analyzed for dissolved organic carbon (DOC) (Shimadzu TOC-500,
Japan) and SS (oven-drying at 105ºC) where the latter was further analyzed for its carbon
and nitrogen content. Twenty-four-hour sampling of the effluent was done to determine
the daily variation of DOC and SS. Dissolved oxygen (DO) and oxidation-reduction
potential (ORP) in the circulation tank were monitored using DO meter (Horiba D-21)
and ORP meter (Horiba D-21), respectively. All analyses were done according to Japan
Industrial Standard (JIS).
Table 1. Composition of food waste used (Standard Garbage – SG)
Components
Wet Weight
Composition
( kg/m3/d )
(% w/w – wet basis)
Vegetables
Cabbage
2.9
18
Carrot
2.9
18
Fruits
Apple
2.2
14
Banana
2.6
16
Meat
Fried Chicken
1.6
10
Rice
1.6
10
Others
Egg
1.6
10
Used Tea Leaves
0.6
4
Total
16.0
100
From the DOC, SS and carbon content data, carbon mass balance was estimated.
Mineralized carbon was estimated by deducting the sum of the cumulative amount of
carbon in effluent from the start of experiment and the amount of carbon in the solid
sample of the solubilization reactor from the total amount of carbon in fresh food waste
supplied.
3. RESULTS AND DISCUSSION
3.1. Effect of Aeration
The colors of SS in effluents were black and brown in Run 1 without aeration and
Run 2 with aeration, respectively. DO in the circulation tank of Run 1 was almost zero
within 24 hours and the average ORP value was -150mv. On the other hand, DO in Run
2 kept increasing within 6 hours after feeding food waste from 0.5 to 4 mg/L and leveled
off. Low DO at the beginning of operation in Run 2 implies that large amount of easily
biodegradable organic matter were initially supplied from the solubilization tank into the
circulation tank and much oxygen was used up for the degradation in the circulation tank.
Figure 2 shows DOC concentrations within 24 hours after feeding food waste.
The large difference between DOC concentrations in Run 1 and 2 means that DOC was
not degraded sufficiently and was discharged under anaerobic condition (Run 2) even
though DOC was easily biodegradable. DOC concentrations in effluent decreased from
an average concentration of 148 mg/L in Run 1 to 26 mg/L in Run 2.
DOC (mg/L)
.
Run 1 (no aeration)
Run 3 (aeration + biofilm)
Run 2 (aeration)
Run 4 (aeration + biofilter)
200
150
100
50
0
0
5
10
15
20
25
30
Time (hr)
Figure 2. DOC concentrations within 24 hours after feeding food waste
Run 1 (no aeration)
Run 3 (aeration + biofilm)
Run 2 (aeration)
Run 4 (aeration + biofilter)
,
2500
SS (mg/L)
2000
1500
1000
500
0
0
5
10
15
20
25
30
Time (hr)
Figure 3. SS concentrations within 24 hours after feeding food waste
Figure 3 shows SS concentrations within 24 hours after feeding food waste. SS
concentrations in Run 2 were higher than those in Run 1. Effluent was discharged from
the mid-depth of the circulation tank preventing oil and large size of SS from
discharging. Aeration in the circulation tank caused the large size of SS settling at the
bottom to be suspended and discharged.
Figure 4 shows the carbon mass balance. Approximately 27 % of food waste was
solubilized (converted to DOC and SS – size less than 2mm) and 33 % was mineralized
in Run 1, however, 42 % of food waste accumulated in the solubilization reactor. When
aeration was applied (Run 2), mineralization was slightly improved from 33 % to 47 %
and almost negligible accumulation of carbon occurred. Therefore, large carbon
accumulation in Run 1 was probably due to the occurrence of anaerobic condition in the
solubilization tank. Tap water and the circulating water are periodically flowed into the
solubilization tank and supply oxygen for the solubilization of food waste.
The
circulating water did not contain oxygen when aeration was not carried out in the
circulation tank. Therefore, oxygen would be deficient for the solubilization of food
waste in the solubilization tank.
DOC
C in SS
C in Reactor
C as CO2
Run 1 (no aeration)
Run 2 (aeration)
Run 3 (aeration + biofilm)
Run 4 (aeration + biofilter)
0%
20%
40%
60%
80%
100%
Carbon (%)
Figure 4. Carbon mass balance
3.2. Contribution of biofilm and biofilter on improvement of mineralization
SS concentrations in effluent decreased by installing biofilm inside the circulation
tank (Run 3) as shown in Figure 3. However, DOC concentrations increased as shown in
Figure 2. Higher DOC in Run 3 than Run 2 was probably due to the insufficient DO.
Although twice as large amount of oxygen was supplied in Run 3 than in Run 2 for the
biodegradation of SS, DO was not detected just after feeding food waste while DO
concentrations just before feeding food waste were less than 2 mg/l. On the other hand,
DO concentration in Run 2 was 0.5 mg/l just after feeding food waste and were around 4
mg/L just before feeding food waste.
It can be seen in Figure 3 that SS concentrations in effluent were significantly
decreased to 17 mg/l on the average and 63 mg/l as maximum by installing biofilter
outside the circulation tank (Run 4). DOC concentrations in Run 4 were almost the same
as Run 2, that is, 28 mg/l on the average and 33 mg/l as maximum. Effluent in Run 4
would not require further treatment in the sewage system.
Run 3 and Run 4 were successfully operated without accumulation of food waste
in the solubilization tank as shown in Figure 4. Around 80 % of food waste supplied was
mineralized in Run 3 by installing biofilm into the circulation tank. Most of the food
waste supplied (98%) was mineralized when biofilter for trapping SS and biodegrading
SS and DOC was installed (Run 4). To compare to the treatment of food waste by
disposers or grinders, the biological solubilization and mineralization system can reduce
organic loading to the sewage system to half by aeration in the circulation tank and 80 %
by installing biofilm into the circulation tank. Moreover, further treatment would not be
required when biofilter is combined with the system.
4. CONCLUSION
The purposes of the study are to operate the biological solubilization and
mineralization process without accumulation of food wastes and to increase
mineralization rate for the reduction of organic loading to the sewerage system.
Biological solubilization and mineralization process was operated without the
accumulation of food waste by aeration in the circulation tank. The process can reduce
organic loading to the sewage system to half by aeration in the circulation tank and 80 %
by installing biofilm into the circulation tank. The process combined with biofilter would
not require further treatment of effluent.
5. REFERENCES
Aoshima, M., Pedro, M.S., Haruta, S., Ding, L., Fukada, T., Kigawa, A., Kodama, T.,
Ishii, M. and Igarashi, Y. (2001). Analyses of microbial community within a composter
operated using household garbage with special reference to the addition of soybean oil, J.
Biosci. Bioeng., 91(5), 456-461.
de Koning, J. and van der Graaf, J.H.J.M. (1996). Kitchen food waste disposers: effects
on sewer system and wastewater treatment, Dept. of Wat. Manage. Environ. Sanit. Eng.
Gallil, N.I. and Yaacov, L. (2001). Analysis of sludge management parameters resulting
from the use of domestic garbage disposers. Wat. Sci. Tech., 44(10), 27-34.
Karrman, E., Olofsson, M., Persson, B., Sander, A. and och Aberg, H. (2001). Food
waste disposers – a technology with sustainability potentials?, VA-FORSK report. 2.
Kreith, F., (1994). Handbook of solid waste management, McGraw-Hill Inc., New York.
Okada, M. and Nishijiam, W. (2001). Solubilization of food wastes by wet compositing,
Environmental Conservation Engineering, 30(11), 855-859.
Sankai, T., Ding, G., Emori, N., Kitamura, S., Katada, K., Koshio, A., Maruyama, T.,
Kudo, K. and Inamori, Y., (1997). Treatment of domestic wastewater mixed with crushed
garbage and garbage washing water by advanced gappei-shori johkaso. Wat. Sci. Tech.,
36(12), 175-182.
Shin, H.S., Han, S.K., Song, Y.C. and Lee, C.Y. (2001). Performance of UASB reactor
treating leachate from acidogenic fermenter in the two-phase anaerobic digestion of food
waste, Wat. Res., 35(14), 3441-3447.
Strutz, W.F. (1998). A brief summary and interpretation of key points, facts and
conclusions for University of Wisconsin study: “life cycle comparison of five engineered
systems for managing food waste”.
Wang, Q., Yamabe, K., Narita, J., Morishita, M., Ohsumi, Y., Kusano, K., Shirai, Y. and
Ogawa, H.I. (2001). Suppression of growth of putrefactive and food poisoning bacteria
by lactic acid fermentation of kitchen waste, Process Biochem., 37, 351-357.
Yun, Y.S., Park, J.I., Suh, M.S. and Park, J.M., (2000). Treatment of food wastes using
slurry-phase decomposition, Bioresource Technol., 73, 21-27.