Challenges of developing anaerobic digestion (AD)

Anaerobic digestion (AD) is a biological process that happens naturally when bacteria breaks down organic matter in the closed system or container with little or no oxygen. Compared to aerobic composting practice that has been developing since the early first century during the Roman Empire, research on AD with the interest in the manufacturing of biogas (methane) has been starting since the 17th century.

Actually both aerobic and anaerobic systems require elemental oxygen for growing and reproducing microorganisms involved in the process of decomposition. In an anaerobic system, the gaseous oxygen is prevented from entering the system through physical containment in sealed tanks. Anaerobes access oxygen from sources other than the surrounding air. The oxygen source for these microorganisms can be the organic waste material itself or alternatively may be supplied by inorganic oxides from within the input material or feedstock.

Construction of the 7-megawatt AD biogas plant, the only base load renewable electricity in the US Virgin Islands on the island of St. Croix will be started in the mid of 2015. The majority feedstock will be giant king grass, although basically almost any organic waste can be processed with AD, including waste paper and cardboard, food waste, industrial effluents, municipal sewage, agricultural and animal waste. Besides biogas for electricity, it will produce a solid and liquid residue called digestate which can be used as a soil conditioner to fertilize land.

That plant will also be a major water reclamation project for the US Virgin Islands, because their agricultural irrigation comes from a secondary treated effluent that is currently being discharged to the ocean; it will be reused for non-food crops production. It is said that the recovered water that would be lost will reduce power bills by up to 5% to the Virgin islander rate payers and the project would create a lot of jobs too.

I have ever compared the cost and benefit between an aerobic system and anaerobic digestion at the tea drink company SOSRO in Java. In general, the process of AD is usually slower in the beginning and more consistent after approaching the optimum conditions. Less space will be needed for AD operation but the investment cost for infrastructure is usually higher than the aerobic system for waste management.

Concerning the operation of AD, it may need more detailed monitoring of the process and quality control of the products. As the main product of AD is biogas methane, the by-product fluffy digestate material can be used as compost mix for plants, animal bedding including compost worms for a better protein production, and for making biopolymers such as an environmentally friendly durable plastic.

Please contact www.burnabyredwigglers.com for the consultation and to set-up the technology of vermicomposting to increase the quality of by-product AD (digestate) before application to the land.

– Bintoro Gunadi

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