Process Design and Assessment of the Performance of Three Macrophytes in a Biorefinery Polishing Partly Treated Sewage in Novel SHEFROL Bioreactors

Abstract

The development of a biorefinery is described based on rapid polishing of partially treated sewage with three different species of macrophytes in the recently developed SHEFROL® bioreactor which functions almost entirely on solar and gravitational energy, requiring no chemicals. It was seen that at a hydraulic retention time (HRT) of just 2 h, suspended solids, COD, BOD, total Kjeldahl nitrogen, soluble phosphorus, zinc, copper, nickel, and manganese are reduced to the extents of 92–95%, 76–78%, 77–81%, 56–61%, 60–66%, 43–46%, 45–48%, 30–35%, and 31–33%, respectively. The treated water meets the water quality standards set for the discharge into surface water bodies. M. quadrifolia was seen to be most effective of the three macrophytes, followed by P. stratiotes and S. molesta, as a sewage cleansing agent, but the difference in the performance of the macrophytes was only marginal, and not highly significant statistically (p ≥ 0.5). The paper also shows that it is possible to extract energy precursors in the form of volatile fatty acids (VFAs) from the harvested macrophyte biomass and then convert the biomass into organic fertiliser. All the steps associated with the closed loop circular biorefinery occur at ambient temperatures and pressures, requiring little consumption of energy and materials, and leaving negligible footprints.