municipal solid waste
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DESCRIPTIONmerupakan copy dari materi presentasi "Biomethanation of Municipal Solid Waste"
MUNICIPAL SOLID WASTE
Salin Kumar Sasi
URBAN WASTE SCENARIO
Urban India generates about 1.4 lakh MT/day of MSW
Requires 1750 acres of land for land filling/year
PHASE I MSW SCENARIO IN INDIA
PHASE II BIOMETHANATION
PHASE III FACTORS AFFECTING
PHASE IV BIOMETHANATION PROCESS
PHASE V BIOMETHANATION OF MSW IN INDIA
PHASE VI BIOMETHANATION PLANT IN
ABROAD AND INDIA
PHASE VII RESULTS AND DISCUSSIONS
MSW SCENARIO IN INDIA
TECHNOLOGICAL OPTIONS FOR
ENERGY RECOVERY FROM URBAN WASTES
POTENTIAL OF ENERGY FROM
(lakh tpd)1.48 2.15 3.03
MW 2550 3670 5200
(mcd)17.75 20.70 24.75
MW 330 390 460
As per MSW Rule 2000, biodegradable material
should not be deposited in the sanitary landfill
Therefore there is almost no scope of generation of
biogas in the form of landfill gas from new sanitary
However, there is a huge potential of trapping the
landfill gas generated in the old dump-sites across
the country, particularly the large ones with more
than 5 meter thickness (height plus depth)
MERITS OF BIOMETHANATION
Reduction in land requirement for MSW disposal.
Preservation of environmental quality.
Production of stabilized sludge can be used as
soil conditioner in the agricultural field.
Energy generation which will reduce operational
Supplement national actions to achieve real, long
term, measurable and cost effective GHGs
reductions in accordance with Kyoto Protocol.
Complex process leading to generation of methane and carbon dioxide.
Process involves three steps (Barlaz et al 1990) Hydrolysis Acidification Methanogenesis
Process can be carried out in Single step Two step
Anaerobic bacteria breakdown complex organic molecules (proteins, cellulose, lignin and lipids) into soluble monomer molecules such as amino acids, glucose, fatty acids and glycerol.
Monomers are available to the next group of bacteria.
Hydrolysis of complex molecules is catalyzed by extra cellular enzymes (cellulose, proteases and lipases).
Hydrolytic phase is relatively slow ,can be limiting in anaerobic digestion.
Acidogenic bacteria converts sugar, aminoacids and fatty acids to organic acids (acetic, propionic, formic, lactic, butyric acids), alcohols and ketones (ethanol, methanol, glycerol and acetone), acetate, CO2and H2.
Acetate is the main product of carbohydrate fermentation.
The products formed vary with type of bacteria as well as with the culture conditions (temperature, pH etc).
Acetogenic bacteria converts fatty acids and alcohols into acetate, hydrogen and carbon dioxide .
Acetogenic bacteria requires low hydrogen for fatty acids conversion .
Under relatively high hydrogen partial pressure, acetate formation is reduced and the substrate is converted to propionic acid, butyric acid and ethanol rather than methane.
Methanogenesis in microbes is a form of anaerobic respiration.
Methanogens do not use oxygen to breathe, oxygen inhibits the growth of methanogens.
Terminal electron acceptor in methanogenesis is carbon.
Two best described pathways involve the use of carbon dioxide and acetic acid as terminal electron acceptors:
CO2+ 4 H2 CH4 + 2H2O
CH3COOH CH4 + CO2
Short chain fatty acids
Lipase, protease, pectinase
cellulase, amylase produced
by hydrolytic microorganisms
Stage 1 Hydrolysis
(Carbohydrates, lipids, proteins etc)
Stage 2 Acidogenesis
(mainly acetic and formic acid)Stage 3 Acetogenesis
Acetate CO2 and H2
deamination, ring reduction
and ring cleavage
Carboxylic volatile acids, keto acids,
hyroxy acids, ketones, alcohols,
simple sugars, amino aicds,H2 and CO2
Stage 4 Methanogenesis
Courtesy-Kashyap .D.R et al ,2003
PHASE - III
Lower nutrient requirement compared to aerobic bacteria.
COD:N range is 700:5.
N used in synthesis of Enzymes, RNA, DNA.
Concentration of various nutrients (Speece et. al ,1996)
N : 50 mg/lP : 10 mg/lS : 5 mg/l
Most important process control parameter.
Optimum pH between 6.7 & 7.4 range for methanogenic bacteria (Zehnder et. al. 1982).
Excess alkalinity or ability to control pH must be present to guard against the accumulation of excess volatile acids.
The three major sources of the alkalinity are lime, Sodium bicarbonate and sodium hydroxide.
Constant and Uniform temperature maintenance.
Three temperature range
Psychrophilic range ; < 200 C.
Mesopholic range ; 200 C to 400C.
Thermophilic range ; >400 C.
Rates of methane production double for each 100C temperature change in the mesophilic range .
Loading rates must decrease as temperature decreases to maintain the same extent of treatment.
Operation in the thermophilic range is not practical because of the high heating energy requirement (Ronald L. Drostle 1997)
Study of temperature variation (Alvarez Rene et al 2007).
Forced square-wave temperature variations
(i) 11 0 C and 25 0 C,
(ii) 15 0 C and 29 0 C,
(iii) 19 0 C and 32 0C.
Large cyclic variations in the rate of gas production
and the methane content.
The values for volumetric biogas production rate and
methane yield increased at higher temperatures.
The average volumetric biogas production rate for
cyclic operation between 11 and 25 0C was 0.22 L d -1 L -
1 with a yield of 0.07 m 3CH 4kg -1 VS added (VSadd)
Between 15 and 29 0C the volumetric biogas
production rate increased by 25% (to 0.27 L d -1L-1with
a yield of 0.08 m 3CH 4 kg -1 VSadd).
Between 19 and 32 0C, 7% in biogas production was
found and the methane yield was 0.089 m3 CH4 kg-1
Digester showed an immediate response when the
temperature was elevated, which indicates a well-
maintained metabolic capacity of the methanogenic
bacteria during the period of low temperature.
Periodic temperature variations appear to give less
decrease in process performance than as prior
Courtesy- Alvarez Rene et al 2007
SOLID RETENTION TIME (SRT) AND
HYDRAULIC RETENTION TIME(HRT)
SRT is defined as the average time the solid particles
remains in the reactor.
The anaerobic digestion is typically performed in
Continuously Stirred Tank Reactor (CSTR).
The performance of CSTR is dependent on hydraulic
retention time (HRT) of the substrate and the degree of
contact between the incoming substrate and a viable
bacterial population (Karim et al.,2005).
An increase or decrease in SRT results in an increase or
decrease of the reaction extent.
Mixing creates a homogeneous substrate preventing
stratification and formation of a surface crust, and
ensures solids remain in suspension.
Mixing enables heat transfer and particle size reduction
as digestion progresses .
Mixing can be performed in two different ways(Kaparaju
P et al,2007):
Continuous mixing SRT is equal to HRT
Non-continuous mixing SRT is more than HRT
The effect of continuous , minimal (mixing for 10 min
prior to extraction / feeding) and intermittent mixing
(withholding mixing for 2 hr prior to extraction/feeding)
on methane production was investigated in lab-scale
CSTR (kaparaju P. et. al ,2007) .
On comparison to continuous mixing, intermittent and
minimal mixing strategies improved methane
productions by 1.3% and 12.5%, respectively.
Calcium, magnesium, and ammonium
bicarbonate are examples of buffering substances
found in a digester .
A well established digester has a total alkalinity
of 2000 to 5000 mg/L.
The principal consumer of alkalinity in a reactor
is carbon dioxide .
Toxicity depends upon the nature of the substance
, concentration and acclimatization .
NH 4-N concentration of 1500-3000 mg/L at 200C
and pH 7.4 and above is considered stimulatory .
Anaerobic process is highly sensitive to toxicants
due to slow growth rate.
BIOMETHANATION INCLUDES FOUR