Treating anaerobically digested piggery effluent (ADPE) using microalgae in thin layer reactor and raceway pond

The successful cultivation of microalgae on anaerobically treated wastewaters would not only allow for the bioremediation of the waste stream but also the cost effective production of algal biomass. In this study, the growth and bioremediation ability of a microalgal consortium of Chlorella sp. and Scenedesmus sp. for treating anaerobically digested piggery effluent (ADPE) was assessed and compared using a thin layer reactor (TLR) (0.5-cm depth, 350 L) and a conventional raceway pond (15-cm depth, 1500 L) with an initial ammonium concentration of 110 +/- 10 mg N-NH4+ L-1. The ammonium removal rate of microalgae grown in the TLR (19.23 mg N-NH4+ L-1 d(-1)) was 1.4 times higher than that grown in the raceway pond. The ash-free biomass yield (0.84 g L-1) and the average volumetric biomass productivity (60 mg L-1 d(-1)) of the algal consortium in the TLR were 2.5 and 2 times higher than that achieved in the raceway pond, respectively. However, considering four times higher culture volume in the raceway pond, the average areal biomass productivity in the raceway pond (4.2 g m(-2) d(-1)) was more than two times higher than the productivity achieved in the TLR (1.9 g m(-2) d(-1)). As a result of this, the areal lipid productivity of the microalgae grown in the raceway pond was also 2.7 times higher than that grown in the TLR. Our results indicated that under the operational conditions evaluated in this study and based on areal biomass productivity, raceway pond performed better than the thin layer reactor for treating ADPE.