Our Product & Services
What We Provide....
Anaerobic digestion (AD) is a treatment for wastewater in the absence of oxygen, producing biogas that can be used to generate electricity and heat. Wastewater treatment using anaerobic process is a very promising technology, which presents extremely interesting advantage compared to the classical aerobic treatment. Green & Smart Sdn Bhd has started doing anaerobic treatment since 1972 and tank digesters from 1984 and built many types of anaerobic treatment system (like UASB, complete mix, contact type, etc) successfully, as turnkey contractors.
For palm oil mill effluent, Green & Smart Sdn Bhd has developed POME-MAS™(Palm Oil Mill Effluent-Mesophilic Anaerobic System) technology, which is different from existing technologies. This will give higher COD reduction efficiency and higher yield of biogas.
Ahead of the competition, G & S is continuously conducting research on the anaerobic treatment.
We will take the Palm Oil Mill Effluent (POME) after the last cooling pond. After removing most of the fiber and broken nuts, it will be pumped to a holding tank where it is well homogenized. Then, the effluent will be pumped into closed anaerobic reactor tanks.
The enclosed anaerobic reactor will operate under mesophilic condition at 30°C-40°C under fully mixed condition. The overflow from digester will go to a settling tank. The supernatant will go to aeration ponds for further treatments. The settled sludge will be recycled to the digesters or send to sludge drying bed.
The biogas from the top of the reactors will go to an automatic CDM compliant closed flare (GREEN-FLARE™). Here all methane must be destroyed before going out of flare chimney; the exhaust temperature maintained above 550°C always.
FEATURES OF OUR SYSTEM:
With our 26 years of anaerobic digestion with 30 over reactors in many countries, we have managed to develop POME-MAS™ specifically for palm oil mill effluent (POME). At present, there are 12 reactors running in FELDA mills. They are of various sizes ranging from 1500 cubic meter to 5000 cubic meter. They are running satisfactorily since 2009. The COD reduction efficiency is from 89% to 95% as can be seen in client’s Acceptance Test Letter. Client tested each rector with its design hydraulic capacity for 24 hours for 12 continuous days. The test were carried out by client and certified by them. Unusual shock loads were sustained well and reactors recovered quickly. We believe we can achieve consistent COD reduction efficiency above 92% (BOD reduction 95% to 97%) with proper supervision and operation.
Gas production is consistent and methane (CH₄) content varies between 60%-75%. Sample tests of H2S shows values between 600ppm to 1000 ppm at flare inlet.
The higher the COD reduction efficiency, higher will be the gas production. This will give higher power production and more revenue.
OUR CREDENTIALS ON BIOGAS PROJECTS
We have commissioned more than 30 anaerobic reactors since 1984 until now, out of that, 12 are for POME. We also have different types of wastewater treatment plants. Our digesters are supplying gas to boilers consistently at Carlsberg Brewery, Shah Alam; Mohan Brewery, India and Heveafil, Batang Kali for more than 10 years, where they are connected to dual fuel burners. Biogas can be used as fuel for gas engine to generate power.
- COD reduction efficiency of POME-MAS™ reactors 2, 3 and 4 for Palm Oil Mill 1 on July 2009
- COD reduction efficiency of POME-MAS™ reactor 1 for Palm Oil Mill 2 on November 2010
- COD reduction efficiency of POME-MAS™ reactor for Palm Oil Mill 4 on June 2009.
- COD reduction efficiency of POME-MAS™ reactor 2 for Palm Oil Mil 2 on December 2010
- COD reduction efficiency of POME-MAS™ reactor 1 for Palm Oil Mill 3 on May and Jun 2010
Description of a Covered Lagoon Digester
A cover can be floated on the surface of a properly sized anaerobic lagoon receiving POME to recover methane. The most successful arrangement includes two lagoons connected in series to separate biological treatment for biogas production and storage for land application. A variable volume one-cell lagoon designed for both treatment and storage may be covered for biogas recovery. However, a single-cell lagoon cover presents design challenges not found in constant-volume lagoons and will require assistance of professionals familiar with the design, construction and operation of these systems.
The primary lagoon is anaerobic and operated at a constant volume to maximize biological treatment, methane production, and odour control. The biogas recovery cover is floated on the primary lagoon. Ideally, POME contaminated runoff is bypassed to the secondary lagoon. The secondary lagoon is planned as variable volume storage to receive effluent from the primary lagoon and contaminated runoff to be stored.
Temperature is a key factor in planning a covered lagoon. Warm climates require smaller lagoons and have less variation in seasonal gas production. To compensate for reduced temperatures, loading rates are decreased and hydraulic retention time (HRT) is increased. A larger lagoon requires a larger, costlier cover than a smaller lagoon in a warmer climate. Reduced methane yield may decrease the return on investment.
Ponding or Lagoon System is counted for 85% of the total treatment plant in Malaysia, it has different stages, for examples Cooling Pond, Anaerobic Pond, Facultative Pond, Acidification Pond, Aerobic Pond, Stabilization pond etc. Anaerobic digestion is final discharge requiring BOD to comply with discharge standards (either into stream/ land application). Types of final discharge, are Continuous Discharge lagoon (Most commonly used), Controlled Discharge lagoon, Hydrograph Controlled Release lagoon and Complete Retention lagoon. The depth of each pond determines its function. Typically, easy construction and maintenance due unsophisticated technology. Does not require mechanical mixing but large land space required. Direct emission Green House Gas .
Understanding Anaerobic Digestion
Consist of 4 main stages ( Hydrolysis, Acidogenesis, acetogenesis, methanogenesis) .
In the hydrolysis phase, water reacts with long-chain organic polymers such as polysaccharides, fats, and proteins to form soluble shorter-chain polymers, such as sugars, long-chain fatty acids, and amino acids. Cellulose, amylase, lipase, or protease - enzymes produced by microorganisms - perform this process.
During the acidogenesis phase, anaerobic oxidizers use the sugars, long-chain fatty acids, and amino acids created during hydrolysis as substrates. A wide variety of different bacteria perform acidogenesis. Acidogenesis is often the fastest step in the conversion of complex organic matter during liquid-phase digestion. In a stable anaerobic digester, the main degradation pathway is via acetate, carbon dioxide, and hydrogen. The bacteria respond to increased hydrogen concentrations in the liquid by producing lactate, ethanol, propionate, butyrate, and volatile fatty acids (VFAs), which the methanogenic microorganisms use as substrates.
In the acetogenesis stage, hydrogen-producing acetogenic bacteria convert fatty acids and ethanol/alcohol into acetate, carbon dioxide, and hydrogen. This intermediate conversion is crucial for the successful production of biogas, since methanogens cannot use these compounds directly. Acetogens grow slowly and depend on a low partial pressure of hydrogen for acetogenic degradation to yield energy. Acetogens are sensitive to environmental changes; they require long periods to adjust to new environmental conditions.
During the methanogenesis stage, methane forms by two main routes. In the primary route, the fermentation of acetic acid, the major product of the acid forming phase, produces methane and carbon dioxide.
- Sewage Treatment Plant with GRASS Reactor
Ideal condition for anaerobic digestion
Mesophilic range (25–40°C) & Thermophilic range (50–60°C).Biogas plants usually prefer the mesophilic range because the thermophilic range requires a stricter temperature-control system. Digesters should maintain temperatures above 20°C for optimal production of methane. Rates of methane production approximately double for each 10°C increase in temperature in the mesophilic range. Physical parameters such as viscosity and surface tension change with temperature. Thermophilic temperatures result in better mass transfer and a higher digestion rate than mesophilic conditions. A stable temperature achieves better results than fluctuating temperatures.
pH & Buffering system
pH ranges of 6.5–7.5 results in good performance and stability in anaerobic systems which is suitable for bacteria involved. To guard against the accumulation of excess volatile acids, system operators must prevent pH from becoming too acidic. Lime, sodium bicarbonate, and sodium hydroxide, three major chemical sources of alkalinity, can provide this buffer. Most POME applications, however, and especially covered lagoon technology, do not require chemical dosing to neutralize pH. Anaerobic effluent water contains buffer alkalinity from bicarbonate (HCO3); recirculating the effluent water to the raw POME collecting tank maintains a neutral pH.
Process design parameters such as the area of the liquid-gas interface, the stirring rate, and the temperature of the liquid (which influences the viscosity and surface tension) affect the liquid-to-gas phase. Typically, gases form at a much higher rate than that of the liquid-to-gas transfer, resulting in high concentration of gas in the liquid. Overconcentration of certain gases such as CO2 and H2S may cause a drop in pH, affecting the biological processes.
Provides good contact between substrate and microbes, ensure the temperature is uniform, reduce resistance to mass transfer, minimized build-up of inhibitory intermediate and stabilizes environment conditions.In research of Kim.M et al (2002) & Choorit W. et al proved that mechanical mixing enhanced COD removal rate & production of methane Nutrients.
Of all the microorganisms in anaerobic digestion, methanogens are commonly considered the most sensitive to toxicity. The toxicity of NH3, H2S and VFAs depends on pH. In un-adapted cultures, a free NH3 level of 150 mg/l can inhibit methanogen growth. Methanogens can tolerate much higher concentrations, however, if the culture has adapted gradually. NH3 is toxic at pH levels greater than 7. H2S and VFAs are toxic at pH levels less than 7. Concentrations of up to 200 mg/l of H2S do not inhibit growth, but the mixture may emit a strong smell from the hydrogen sulphide.Methanogenic bacteria are also sensitive to oxygen. In the mixed culture in an anaerobic digester, facultative anaerobic bacteria constitute some of the hydrolyzing and acidogenic bacteria that consume oxygen present in the digester.
biodegradation requires available nutrients including nitrogen, phosphorus and trace elements (micronutrients). Nutrients build cells that form microorganisms and produce biogas. General chemical elements that form microorganisms are carbon (50%), oxygen (20%), nitrogen (12%), hydrogen (8%), phosphorous (2%), sulphur (1%), and potassium (1 %). Generating biogas requires a carbon-to-nitrogen ratio of at least 25:1 Macro: C,H,O,N,S,P,K,Ca,Mg- provides food Micro: Fe, Ni,Zn, Mn, Mo,Co- Keeps healthy
Organic Loading Rate(OLR)- (kg COD/m3.d)
Is the measure of the anaerobic digestion biological conversion capacity. Indicates how many kilograms of organic dry solids are loaded per m3 of digester volume and with unit of time.For a lagoon system the OLR ranging from 1.4 to 2.5.Tank system able to handle high organic loading rate which is 2.0 – 5.0. It leaves significant impact on gas production where increase of with OLR until a stage when methanogen bacteria could not work quick enough to convert acetic acid to methane which in return increased hydrogen partial pressure concomitantly decreased the methane yield (H.Patel et. al, 2002)
Anaerobic lagoons are essentially covered ponds equipped with mixing mechanisms. This design normally handles a solids content of less than 2%, and operates in the mesophilic temperature range. Most commonly used system, low cost compared to CSTR. Anaerobic system emits higher amount of methane compared to open digester tank with average methane composition of 54.4%, reduces the use of auxiliaries e.g. pumps