PROPOSED RM100 MILLION ANAEROBIC DIGESTION OF PIG WASTES PROJECT

News is in the air now that the Selangor State Government is proposing a centralized pig rearing industry somewhere in Sepang and that there will be a centralized pig wastewater treatment estimated to cost about RM100 million dollars. There must be excitements among contractors and vendors trying to secure the project! After 100 million 0.1 billion worth of money. Its a lot of money and the cost of building such mega anaerobic digestors would probably look easy on paper than in reality. It is very easy to build very large anaerobic digesters but it would not be easy to operate and maintain the process efficiently as the anaerobic digestion process is known for its sensitivity, process fluctuations and lack of stability. I wonder if the marketting people promises the moon in order to get the contract or will the State government will end up with a white elephant project? And the people surrounding the rearing site will still face air and water pollution from the pig generation activities?


Rearing pigs is a dirty business! Everybody knows that pigs generate a lot of wastes mainly through their faeces and urine. It is further compounded by the volume of wasted feed that end up in the wastewaters, Pig slurry is often characterised by very high BOD, COD, Solids and high ammonia and phosphates. It is the Armageddon of wastewater treatment

I feel concerned over the wastewater project being offered to the successful companies just based on a few visits by state representatives who probably knows next to nothing about wastewater treatment of pig slurry and bowled over by the platinum services given throughout their stay and site visits to these holiday spots. It makes me wonder how much they really see or understand the process. Secondly, the data or slide shows being generated to show to the invited guests from from our countries are perhaps too idealistic and does not reflect the reality.

I do hope our state counselors who endorse this project will learn from examples of failed projects almost similar nature.
My suggestion to the state government is that:

1 They must select their own experts who understand and foresee the problems of such ventures and be accountable for failure if any
2 The company being awarded the contract must provide real proof or carry out feasibility studies including scale ups to show that the proposed process is working in reality and not just on paper
3 Such studies should use our own pig wastes and under real conditions

Do not award the tender if these conditions are not fulfilled as it can be a source of embarrassment in the next general elections
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HARNESSING METHANE GAS FROM LANDFILLS

In times of energy shortage and increasing pollution by wastes, many companies have toyed with the idea of extracting methane as a fuel from the tons and tons of waste filling the landfills. In theory this idea seems to be very very attractive. However in reality, this idea might not be technically or economically viable. There are many problems that will be faced in attempting to produce and extract methane from landfill compared to doing anaerobic digestion in proper digesters

WASTE COMPOSITION AND PRESENTATION
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In normal anaerobic digesters the type and composition of wastes fed into the digestors can roughly be controlled, in terms of BOD loadings and HRT. This is not so in landfills. In landfills the wastes filling the landfill anaerobic bioreactor are of unknown composition. Most of these wastes are not amenable to anaerobic digestion as they consist of solid wastes made up of yard wastes, plastics, polystyrenes. Their loading rate and organic load could not be ascertained. As reported in previous blog here, some of the wastes in landfills are still not degraded after several decades

LANDFILL BASICALLY SSF
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Compared to conventional anaerobic digesters, landfills are basically SSF or exhibit Solid Substrate fermentation. This will mean that that there will be not much liquid in SSF fermentation.

Anaerobic digestion usually perform well in high liquid environment where not only will it prevent oxygen diffusion but water is a necessary requirement for the nutrient supply and the growth of microorganisms. In fact a few studies in landfills show better decomposition if the landfill leachate is recycled.

LONG RETENTION TIME
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In a normal operating anaerobic digesters treating sewage sludge it is shown that a long retention time of around 10 to 15 days is good for anaerobic digestion. In landfills this is much more longer as the landfill digester is not optimally designed as an anaerobic digester to produce methane. Thus in terms of methane production landfills are not technologically efficient process.
There will be a long slow rate of methane production stretching for years which economically not viable

BATCH REACTOR
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Most anaerobic digesters are operated fed batch wise with HRT about 10 to 15. Landfill bioreactors are more effective as batch reactors functioning more as tombs continually taking the solid wastes until filled to the brim or even above the level of the earth

BIGGEST REACTOR AND SPREAD WIDELY
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If we consider landfills as the biggest bioreactor compared to conventional anaerobic digesters, it will be difficult to mix or improve the mass transfers due to its sheer size. There are many points to consider where to collect the gases or prevent loss of methane gases. It is generally accepted that the loss of methane gas through landfills account to about 30 to 40%. This is economically unacceptable in any methane generating bentures. Technology of methane recovery in landfills has much to be desired.

DIFFICULTY IN MAKING HIGH RATE DIGESTION
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To be commercially successful, anaerobic digesters need to be operated as High Rate digesters. This require stirring and mixing and letting the anaerobic digestion occurring in the thermophilic range is this possible in landfills?

We all know that anaerobic digestion is a very sensitive and instable process and require close monitoring and control. Is this possible in landfills anaerobic digesters? Read more!

ANAEROBIC DIGESTORS- OPENING UP PANDORA'S BOX

The use of anaerobic digestion process in biological wastewater treatment has often been hailed as the ultimate answer in the treatment of various types of wastewaters. There are many advantages cited in using this fermentation technology such as wastewater stability, sludge reduction, dewaterability, energy and fertilizers. Yet such attractive technology that is in the dreams of environmental engineers are often the 'nightmare' of wastewater operations,

The sad truth is the anaerobic digestion process is very sensitive and instable process and easily prone to failure..

The failure of control of the anaerobic digestion is often attributed to the failure of understanding the microbiology and biochemistry of the process

ANAEROBIC DIGESTION AS COMPLEX FERMENTATION
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The anaerobic digestion is a very complex fermentation process because:

1 It is a mix culture microbial populations all involving in the process
2 It is made up of two basic groups of microorganisms; acidogens and methanogens with their own physiological attributes requiring their own specific growth requirements but still dependent on each other in the anaerobic digestion process
3 Methanogens are obligate anaerobic bacteria very fragile, slow growers and easily killed by exposure to oxygen and other extreme conditions
4 Complex substrate loading to the anaerobic digestors
5 Very high solid content and complex rheology of the substrate
6 Poor mixing conditions pf most anaerobic digestors
7 Washouts and slug dosings or shock loadings affecting the bacteria
8 Effect of temperature and ph upon the two groups of microorganisms

OPERATION OF ANAEROBIC DIGESTOR AND CLOSE MONITORRING
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Since one of the hall,arks of anaerobic digestion process is its sensitivity and stability, the success of its operation depend on close monitoring of the anaerobic digestion process. The optimu operating characteristics of an optimally run anaerobic digestor are marked by:

1 High volume of gas production
2 High percentage of CH4 to CO2 ratio
3 Neutral pH
4 Very low concentration of TVFA of less than 200mg/litre
5 Presence of short chain fatty acids such as acetic and propionic acids with little or no trace of butyric and valeric acids

The optimal range occurs in a very narrow range thus close monitoring are required to detect any changes and to take detection before the impending disaster

It should be noted that the TVFA profile is not the cause of a digestor failure but symptoms of the inefficient and uncoupling of the anaerobic digestion process between the acidogens and methanogens Read more!

LANDFILL BIOREACTOR- NEW PERSPECTIVE

The present system of using landfills to treat and dispose the mountains of municipal solid wastes generated is not proving to be comprehensive and efficient. These landfills function more as tombs for our wastes rather than as waste treatment centres. The landfills are designed more as engineering mega structures to hold the waste rather than optimizing microbial processes that degrade the solid wastes efficiently. As a waste treatment centre, landfills fare poorly, exhibiting ‘passive’ biological treatment process with very poor biodegradation rates. A recent documentary on a local cable television showed newspapers dumped decades ago in a landfill are not degraded.

Once the landfills reached their maximum capacity to store the solid wastes, it will become a permanent tomb and could not be regenerated as future landfills. Newer landfills have to be found to replace the retired landfills, and this process goes on and on. It will be a matter of few decades before we will be running out of sites to be transformed into new landfills. This is especially so with the rapid increase in population, urbanizations and existing social habits we are practicing.

PRESENT STEPS TO EXTENDING LAND FILL LIFE

At present the approach to solving the shortage of landfills is more from the reduction of the volume of solid wastes that will end up at the landfill. This is achieved by waste reduction, recycling and reusing the wastes. Such activities will only prolong the lifespan of the landfills. While such activities will help it still does not solve the crucial problem of the landfill as it merely reduces the amount of wastes ending in the landfills and not treating the wastes in the landfill. Until such times we can find ways to enhance biodegradation processes in the landfills, the number and volume of landfills in the country will exhibit the cumulative effect!

The poor biodegradation rates that are synonymous with landfills operations occur because no efforts are made to understand the biodegradation processes and how to enhance these processes in the design and operation of landfills.

Efforts must be made now in the planning and building of landfills to include the enhancement of the various biodegradation processes. Now it is not that it is not possible but more due to the unwillingness to incorporate such biotechnology.

BIOPROCESSES IN LANDFILLS

We have to have a change in attitude towards how landfills should be run and operated. All this while we have regarded landfills more as tombs to store our solid wastes rather than as a waste treatment plant. At present the landfills are not designed or operated to maximize microbial degradations. Existing landfills show very slow rate of biodegradation than anticipated. We need to make landfills more efficient in treating the solid wastes by converting the landfills as landfill bioreactors. The failure to optimize the biological decomposition of solid wastes stemmed from the design and operation of landfills that retard biodegradation processes.

The two basic biodegradation processes occurring in landfills are composting and anaerobic digestion processes. Composting process depends on a good supply of air or oxygen and high moisture content. In landfills, composting could not occur efficiently due to compactions of solid wastes which prevent sufficient supply of air in the compacted wastes. Composting process is important in helping breaking down the large organic particles into smaller fragments which will be easily broken down by further microbial actions.

Anaerobic digestion process is the breakdown of organic matter by various types of microorganisms in the absence of oxygen. This process will occur deep within the layers of the landfills. It is however a very slow and sensitive process and easily destabilized.

These two biological processes do occur in the landfills but are not efficiently carried out due to lack of interest in the landfill operators to monitor, control and optimize the processes.

PARADIGM SHIFT IN LANDFILL OPERATION

What we really need now is a paradigm shift and to regard the landfills more as a waste treatment plant and not as a waste storage centre. To achieve this we need to treat the landfill as a ‘landfill bioreactor’ where the microbial processes in the landfill is enhanced by applying the knowledge of Industrial microbiology and Fermentation technology.

In this aspect the engineers that design and operate the landfills must be amenable to inputs by environmental and industrial microbiologists and fermentation technologists to convert the ‘storage landfills’ to become ‘bioreactor landfills’

THE CONCEPT OF LANDFILL BIOREACTOR

The operation of the landfills as an industrial process is not difficult to envisage. As it is now there are a lot of biotechnology industries which utilizes fermentation technology to produce products by using large scale fermentors or bioreactors. Even now, most biological wastewater treatment plants utilize microorganisms grown in large bioreactors such as activated sludge systems and anaerobic digesters to treat various effluents.

A bioreactor is not any ordinary vessel but a specially designed vessel that is designed to cultivate high concentration of microorganisms and bioconversions. In most high rate bioreactors or fermentors, this is achieved by providing a stirrer to ensure good mixing and mass transfers between the substrate and the microorganisms. There are also physical and chemical sensors to monitor and control the bioreactor

The difference between landfill bioreactors compared to other conventional biological wastewater treatment bioreactor is that the landfills bioreactors are larger and uses solid substrate fermentation instead of liquid substrate. The landfill bioreactor is more complex in operating than the conventional biological wastewater treatment reactors due to the volume and complexity of wastes that it is receiving and treating

A landfill bioreactor is a logical extension in attempts to treat solid wastes more efficiently. In the last decade there are attempts to using landfills bioreactors in Unites States as well as the European countries and the results have been more than encouraging.

ADVANTAGES OF LANDFILL BIOREACTOR

There are several distinct advantages that the bioreactor landfills have over conventional landfills. A landfill bioreactor is more effective in treating solid wastes as there is a more complete and faster rate of biodegradation compared to those occurring in typical landfills. This will result in additional capacity for the landfills and the extension of the lifetime of the landfills. There will be a deferment in the need for new and additional landfills and more profit for the operators.

Lesser leachate will be released by the bioreactor landfills to the environment as the leachate will be recycled back into the landfills to promote faster biodegradation. Less cost will be incurred in treating lower volume of leachate from landfills

More methane gas will be generated within shorter time from the landfill bioreactors which can be exploited as alternative energy resources.

The shorter treatment time and higher stability of wastes achieved through landfill bioreactor will ensure shorter periods of care after the landfills are closed. The stabilized wastes of the landfills will be lesser risks to the environment compared to conventional landfills.

OPERATING A LANDFILL BIOREACTOR

The design and operation of the bioreactor landfills will be different from the ‘hands off’ operation of existing landfills. In traditionally operated landfills used as storage facilities there are attempts to fill as much wastes that can be filled and compacted into the existing landfill before a new cell is opened up. Usually each landfill that has received its total daily load is covered with a layer of soil before the next loading is due. New landfill cells are only opened up and used after existing cells have reached their capacity.

In the operation of bioreactor landfills, the design and operation of the landfills will differ significantly and may even appear as opposing the trends of running conventional landfills.

A bioreactor should be operated as a waste processing facility. The bioreactor landfill should be designed and built to promote the growth of the various microbes involved. Proper understanding of the biodegradation process, the involvement of various physiological groups off microorganism and how to provide the optimum environment for these various groups of microorganisms need to be understood. Close monitoring and control of the bioprocess of the landfill is involved

COMBINATION OF BIOREACTORS NEEDED

The biodegradation process in a landfill bioreactor is made complex by the involvement of various types of microorganisms, complexity of wastes to be treated. The complete biodegradation of the solid wastes require a succession of different organisms of different physiological requirements. A single landfill bioreactor could not possibly provide conditions that are optimal for all the organisms.

There is the need to create a series of landfill cells to optimize the conditions at all the major steps of the bioconversion process in a rotating sequence.

Unless the existing operators of landfills are not willing to implement the technology of landfill bioreactors instead of the conventional landfills, solid wastes will continue to accumulate and more landfills will be needed. At the end of the day when the lease of operating the landfills is over, it will be poor taxpayers who will be footing the bill to repair the environmental damages caused by the derelict landfills! And the bill will not be cheap….!

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