Solid – Liquid separation of dairy manure: Distribution of components and methane production

Chemical treatment and screening can be an effective technique for separation of dairy cattle manure into a liquid fraction (LF) and a nutrient-rich solid fraction (SF). The optimum loading of a strong cationic polyacrylamide was found to be 43.9 g kg−1 of dry excreta. The separated SF contained 29.1% of the initial mass present in the manure and the chemicals added. The Volatile Solids (VS)/Total Solids (TS) ratio, which was 0.78 for the manure, rose to 0.82 for the SF and decreased to 0.63 in the LF. Furthermore, the SF retained 76.1, 79.9, 59.4 and 87.4% of TS, VS, Total Kjeldahl Nitrogen and Total Phosphorus, respectively. In the LF, the ratio of filtrate chemical oxygen demand (CODfiltrate) and COD due to volatile fatty acids (CODVFA) in relation to total COD (CODT) were 0.86 and 0.76, respectively. The percentage of anaerobically biodegradable chemical oxygen demand (CODBD) for the LF was 83.0%. Treatment of the LF in high loading anaerobic reactors would be possible due to these COD characteristics. Specific methane production in terms of VS for the separated LF was 0.580 m3 kg−1. For dairy manure and SF, it was 0.320 and 0.258 m3 kg−1, respectively.

► Chemical treatment is an effective technique for separation of dairy manure.
► Solid fraction retained 59.4 and 87.4% of Nitrogen and Phosphorous, respectively.
► Anaerobic biodegradability of liquid fraction much higher than that of raw manure.
► Characteristics of liquid fraction allow its treatment in high load systems.