Biogas Generation from Rice Cooking Wastewater

Journal of Environmental Treatment Techniques

2020, Volume 8, Issue 2, Pages: 794-796

J. Environ. Treat. Tech.

ISSN: 2309-1185

Journal web link: http://www.jett.dormaj.com

Biogas Generation from Rice Cooking Wastewater

Nadim Reza Khandaker*, S M Shabab Islam, Umme Farah Shakin

Department of Civil and Environmental Engineering, North South University, Dhaka, Bangladesh

Received: 13/08/2019

Accepted: 16/04/2020

Published: 20/05/2020

Abstract

Rice is the staple of all families of South Asia and South East Asia. The process of cooking rice involves boiling the rice in water which

leaves a byproduct of decanted liquid. The research showed that the wastewater generated from cooked rice could be used to generate biogas

with a biogas generation potential of 190 ± 46 mL/g BOD (5.38 ± 0.75 L of biogas/per L of Maar) with the methane content of 78 %. First

order reaction defines the kinetics of biogas production with the intent of fitting between modelled and observed data (r ) of 0.961. The first

order kinetics constant “k” was determined to be 0.2 d . Further a family of four produces 1.0 L of starch rich wastewater per day that has

the potential to produce 5.38 L of biogas with 78 % methane content. Further a household reactor was built out of recycled plastic chemical

drum seeded with cow dung fed with waste rice cooking wastewater handling the wastewater decanted from the daily rice cooking for a

family of five. The biogas generated was used as demonstration to fire a biogas household burner. The experimental program shows the

potential for the use of starch rich wastewater in an urban setting to augment the energy needs for cooking.

Keywords: Biogas generation potential, Cooked rice decant wastewater, Kinetics

Introduction¹

The overall intention of the experimental program was to

introduce domestic rice wastewater in the energy diversification

to stride for sustainable development of South Asian and East

Asian countries future and to identify a source which is readily

available can produce a positive sustainable solution at the

household level.

Bangladesh is a country whose economy is natural gas driven.

Natural gas is used for electricity generation, fertilizer production,

process heating, electricity generation, and household cooking.

About 70% of Bangladesh’s energy demand is met through

natural gas but in recent times, the demand of natural gas has been

exceeding the supply (1). The government has started to put in

place measurers that limit supply. Natural gas supply has been

limited for domestic use placing an undue burden to the urban

population. However, amidst all the crisis, we may have found a

simple potential solution from a very unlikely source in the form

of wastewater generated from rice cooking that serves as the

substrate for biological methane generation. Rice is a staple food

in Bangladeshi households. People rely on it as the chief source

of their dietary needs at least twice per day. The process of

preparing rice involves boiling it in water and this process gives

off a white starchy liquid which is referred to as “Bhaather Maar”,

and in this study this rice rich wastewater was used to conduct a

Biological Methane Potential (BMP) study (2) to ascertain how

much biogas can be produced from waste water generated from

rice cooking. In a controlled experimental program wastewater

generated from cooking rice was characterized, using methane

generating reactors at the bench scale a BMP study was conducted

to ascertain the quantity and quality of the biogas generated from

Maar. The study was further expanded to actual application where

a waste acetone empty plastic drum was converted to a biogas

generator and installed in a urban house as a field trial. The

generated biogas was used to fire a household level cooking

burner to demonstrate the practical efficacy of using waste cooked

rice water to produce biogas for domestic use.

2 Materials and Methods

Raw wastewater: The rice cooking wastewater was obtained

from actual wastewater generated from cooking rice in a typical

household of urban Bangladesh, in average 1.0 L of rice

wastewater is generated per day from a family of 4 persons. A

seven-day composite sample was used to characterize the

wastewater used in the study.

Seed: The BMP study seed was seven-day old crow dung

and for the pilot reactor the seed source was fresh cow dung.

Analysis: The rice cooking wastewater was analyzed for

COD, BOD , TS, and pH as per standard methods (4). The biogas

generated was measured using the piston displacement method

where the piston in the syringe reactor moves up with daily biogas

production the displacement volume is noted by reading off the

gradation lines existing in the syringes used as the BMP reactors

(3).

BMP Reactor Configuration: The bench scale BMP reactor

were 150 ml plastic disposable syringes with a liquid volume of

20 ml (Figure 1). The BMP syringe reactors were operated as

batch rector with an incubation period of 34 days. In the BMP

study the rice wastewater was fed directly to the reactor at the

initiation of the study. The food to microorganism ratio (F/M) for

the BMP study was 0.02. The daily biogas production was

Corresponding author: Nadim Reza Khandaker, Department of Civil and Environmental Engineering, North South University, Dhaka,

Bangladesh. E-mail: nadim.khandaker@northsouth.edu.

Journal of Environmental Treatment Techniques

2020, Volume 8, Issue 2, Pages: 794-796

monitored and noted and at the end of the study the biogas quality

was measured in terms of methane and carbon dioxide

percentage. The data generated was plotted and modelled using

Spreadsheet in accordance to established protocols modelling

anaerobic transformation substrates (4, 5, 6, 7, 8).

Results and Discussion

In line with research trends of using easily biodegradable

wastewater to produce bioenergy (9, 10), the research program

investigated the use of rice cooking wastewater rich in starch

to produce biogas for cooking in domestic houses. The

composite rice cooking wastewater characterized and used in

the study is given in Table 1. This a highly biodegradable

wastewater with high BOD , wastewater and should be very

suitable for methane generation an anaerobic process. The

BMP study conducted using the rice cooking starch

wastewater using syringe reactor seeded with cow dung at an

5 5

F/M ratio of 0.02 at a BOD loading rate of 0.5 Kg BOD /m

within the range of operation of low rate reactors for anaerobic

wastewater treatments currently being designed and

constructed (2).

Figure 1: Syringe reactor used in the BMP study

Table 1: Characteristics of the rice cooking wastewater used

in the BMP study

Field Trial: The field trial reactor was a 100 L waste acetone

drum with to witch two ports retrofitted to be the feed port which

had a feed tube going to the bottom of the drum (Figure 2). The

biogas was vented through a line in the cap of the second port and

directly connected by a quarter inch gas hose pipe to a biogas

home burner. The reactor was operated in a batch feed mode with

daily feeding of the race starch wastewater. The initial seed

volume was 15 L of 5% solids cow dung slurry. The reactor was

operated till the methane content of the biogas was sufficiently

high enough to sustain the flame in the burner.

BOD₅

(mg/L)

Density

(g/ml)

(mg/L)

fraction

(%)

8.3 ±

0.1

23450 ±

796

0.95 ±

0.01

0.47 ±

0.01

98.7

The biogas production trends for the BMP reactors are

shown in Figure 3. From the onset the BMP reactors producing

biogas and gas production was completed within 15 days of

operation. The mean ± Standard Deviation total biogas

production for the four reactors in the BMP test was 190 ± 46

mL/g BOD (5.38 ± 0.75 L of biogas/per L of Maar). Also the

biogas production trend showed that the system did not require

any period of acclimation prior to achieve the high degree of

waste stabilization shown by rapid biogas production

indicating that Maar is easily degradable by the anaerobic

culture. The kinetics of biogas production by the degradation

of Maar by the anaerobic microorganism is defined by Figure

. The Figure shows that first order kinetics curve fitting of

predicted verses observed biogas production using Equation 1

to calculate the theoretical biogas production trend using the

optimized by curve fitting of the first order rate coefficient “k”

value of 0.2 day . The goodness of fit data between the

modelled data and the experimentally observed data showed a

very good fit (r = 0.961).

Biogas

= Biogasmax x (1-e^-^k^t

)

(1)

is biogas at any time in ml biogas/gBOD

where Biogas ,

Biogas is maximum biogas production in ml biogas/gBOD

, t

is time in days, and k is rate constant, day . The time to reach

max biogas production was 2.4 days a short time frame

indicating that the Maar is easily anaerobically biodegradable

and the system has the microorganism to readily degrade the

rice cooking wastewater and produce biogas. The methane

content of the biogas measured in the end of the test was 78%

showing that the biogas generated from Maar has high methane

content close to that of methane gas supplied to household the gas

supply companies. In the field trial reactor, the gas production

was observed within three days of feeding after reactor startup but

the gas produce would not be burn. It was suspected that the

methane content of the biogas was low for we had used fresh cow

Figure 2: Field trial biogas reactor and burner

Journal of Environmental Treatment Techniques

2020, Volume 8, Issue 2, Pages: 794-796

dung to seed the reactor and that the methanogenic population was

not sufficient to produce a high quality biogas with respect to

methane content. After a month of sustained operation, the biogas

produced would burn in a blue flame (Figure 5) indicating that the

produced biogas had methane content sufficient enough to

combust.

In an overall prospective the result of the BMP study and the

field trial showed the potential of Maar a substrate for biogas

production producing a biogas with high methane content. A

waste product such as Maar that is dumped down the drain can be

used in the energy mix to as a source of renewable energy in the

context of south Asia and South East Asia.

Conclusions

The research showed that the wastewater generated from

cooked rice could be used to generate biogas with a biogas

generation potential of 190 ± 46 mL/g BOD (5.38 ± 0.75 L of

biogas/per L of Maar) with the methane content of 78 %. First

order reaction defines the kinetics of biogas production with the

intent of fitting between modelled and observed data (r ) of 0.961.

The first order kinetics constant “k” was determined to be 0.2 d .

Field trial showed the viability of the concept at applied level.

Competing interests

The authors declare that there is no conflict of interest that

would prejudice the impartiality of this scientific work.

Figure 3: Cumulative biogas production with days of operation

Authors’ contribution

All authors of this study have a complete contribution for data

collection, data analyses. Manuscript writing was done by Nadim

Reza Khandaker.

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Figure 5: A blue flame indicating produced biogas had methane

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