Monitoring anaerobic digesters on farms

Abstract

There are 15 anaerobic digesters installed on farms in the U.K. and these were largely stimulated by the opportunity to produce energy coupled with a reduction in slurry odour. A monitoring programme was developed in 1980 to evaluate the average performance of farm plants in terms of net energy production under practical operating conditions. The aim was also to determine the effects of digestion on slurry with regard to pollution reduction and fertilizer value. This paper reports data gathered from one pilot-scale and two full-scale digesters, treating pig slurry, and from one full-scale digester treating dairy cattle slurry. Monitoring showed on full-scale plants, that pig slurry achieved a specific gross biogas production of 0·5 (m 3 biogas)(m 3 digester volume) −1 d −1 and for dairy cow slurry 0·8 (m 3 biogas) (m 3 digester volume) −1 d −1. A pilot plant operating on stored separated pig slurry at a retention time of 8·3 d produced 1·8 (m 3 biogas)(m 3 digester volume) −1 d −1. The biogas yield from the total solids (TS) in pig slurry fed ranged from 0·28 to 0·37 m 3 biogas/kg TS fed. The yield from dairy cow slurry was 0·12 m 3 biogas/kg TS fed. Digester management was found to be important for the successful steady-state operation of digesters on farms. Digester feed solid concentration and feed age were found to influence specific gross biogas production.