Study of optimal conditions in semi-continuous anaerobic co-digestion of table olive effluents and pig manure in a perfectly stirred reactor.

Brines from table olive elaboration were co-digested with pig manure, obtaining high methane productions. In particular, the methane yields obtained for pig manure total solid (TS) initial concentrations of 2%, 7%, 9% (wet basis, wt.) were 106, 213 and 247 mL CH4 gVS-1add, respectively, using mixtures of two types of brine (acid (A) and basic (B)) generated in the elaboration process. Moreover, an experiment with only basic brine was made, using a pig manure TS concentration of 7% wt. In this case, a methane yield of 224 mL CH4 gVS-1add was obtained. The methane production rate was calculated in experiments of 7% pig manure TS concentration and a high kinetic constant of 0.31 d-1 was obtained for the mixture of residual brine. Finally, the effect of Na+ cation concentration was evaluated in the mixture A:B during co-digestion processes with a 7% wt. pig manure TS concentration and inhibition was detected in this process with a [Na+] of 0.56% wt. of the total sample. An energy and economical study on the treatment of these wastewaters by means of anaerobic co-digestion demonstrated a great economic benefit for the producer industry, a reduction in the diesel consumption used to produce its energetic demand and a reduction cost of 3.63 €/m3 generated of A:B brines mixture with ratio 2:1.