Case Study: Going greener with Palmerston North CC's biogas to energy project

An article from NZ Local Government publication, June 2010 - Sustainability is important to Palmerston North residents.

Describes a project to achieve a 400 per cent improvement of the daily biogas production capacity in the existing sludge digesters. The project  was to utilise existing city assets which was both a benefit and a challenge to the project. The two existing municipal sludge digesters at PNCC’s Totara Road plant were installed in the 1960s to treat municipal sludge (primary sludge biosolids). By 2008, tests showed that the mixing efficiency in both PNCC Totara Road digesters was low. The tests showed that PNCC was not achieving more than about 50 per cent of the potential digester biogas production capacity - mainly due to inefficient contact between the sludge bacteria and the primary sludge biosolids.

The costs to upgrade the two digesters to four times the daily biogas production including a new waste reception are in the order of one million. The total cost for this project is approximately $3 million including the generator.

Fast repayment and potential for future earnings comes from three main sources: sales of produced green electricity, a lessened need to buy pipelined natural gas to operate the generator (which will eventually run on 100 per cent biogas) and PNCC’s plan to collect a “gate fee” for receiving new waste materials into its upgraded sludge digester facility. One of the greatest benefits of the improved PNCC Totara Road digester facility is that it can digest a wider range of additional industrial waste including piggery manure, whey waste, grease trap waste, and selected food industry flotation foams. Digesting this waste produces an increase in biogas - which means PNCC ultimately avoids natural gas purchase costs and gets the income stream from collecting the waste in the first place..

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