Nov/Dec Preview: Emerging opportunities for anaerobic digestion energy production

Andrew Mourant

While anareobic digestion projects primarily consist of small-scale applications, this energy alternative still represents an important part of a holistic "environmental" solution.

This article excerpt is taken from the forthcoming November/December edition of Renewable Energy Focus magazine: 

How great a role might micro-producers of sustainable energy play in the grand scheme of things? Nothing could be smaller scale than some of the domestic systems that create biogas from converting organic household rubbish by anaerobic digestion. Yet their significance should not be underestimated.
In India, household anaerobic digesters can provide power for families living hand to mouth, and where electricity supplies are erratic. In Germany, where so much is well organized, they represent commitment to a subsidized renewable energy mix – territory in which the Germans lead most other EU countries by some distance.
What better idea than creating energy while cutting landfill mass and the methane gas emissions that go with it? However, like other renewable technologies, anaerobic digestion can be fraught with complications. There are success stories — but also those of trial and error.
India produces vast amounts of organic household rubbish — World Bank figures suggest 38,350 tonnes per day — and is often very bad at dealing with it (indiscriminate dumping is common). Yet there are many pitfalls when it comes to running efficient energy-producing anaerobic digestion plants.
These are well understood by UK-based waste management expert and environmentalist David Lerpiniere (employed with Ricardo-AEA), who recently returned from a trade mission to India. “The question that kept raising its head — with national and state officials, private developers and NGOs — was whether waste to energy (WtE) is appropriate to address India’s growing solid waste crisis.”
As Lerpiniere explains: “WtE is not a cheap disposal method. It generates energy and can also potentially attract a gate fee, but this needs to balance high operational and maintenance costs, plus payback on a substantial investment. Typically a facility that recovers energy from waste will generate half of its revenue from a tipping fee and half from sales, but is it enough to maintain the plant and generate the revenue needed?”
Still, waste composition is critical, Lerpiniere states. And in India, he notes, it can be hard to get transparency about what happens to waste. “It will involve putting together a lot of pieces to establish anaerobic digestion plants on a bigger scale and make things work.”
Pre-treatment of household waste is, as Lerpiniere notes, “the nub of technical feasibility” for WtE. “We can be fairly certain that waste composition will change. It’s possible to prepare for this by using pre-treatment systems that can be adapted to respond.”
Yet, Lerpiniere notes, there are “excellent examples” in India of good practice for state Governments and municipalities to tap into. Furthermore, the political will seems to be there; the Ministry of Environment and Forests (MoEF) has developed a ‘national master plan’ for developing WtE across the sub-continent.
Biotech, an Indian company established in 1994, is among those exploiting the possibilities of anaerobic digestion at the micro level. It says that well-cared for plants using the right mix of waste should pay for themselves in a maximum of 36 months. However, proper segregation of food and garden waste is one of many hurdles to overcome.
Some of India’s past experiences prove the point. Ten years ago, a high profile anaerobic digestion plant in Lucknow that was designed to handle 300 tonnes of municipal rubbish daily had to close because its technology was defeated by the poor quality of the waste — most of which comprised less than 50-70% inorganic material.
Yet the rewards for getting technology and feedstock right could be enormous. Per Regnarsson, CEO & managing partner at CleanWorldCapital Group Ltd, estimates  WtE plants in India could produce 7,000 MW of power — and the oil energy equivalent of almost 60 million barrels annually recovered from landfill.
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