A pilot-scale assessment of five common weeds in the sustainable treatment of sewage utilizing SHEFROL®, with prospects of a closed-loop biorefinery.

Abstract

Relative efficacy of five common weeds-of the kind that are either rooted in soil or which freely float over water-was assessed in rapid, effective and sustainable treatment of sewage at pilot plant scale in the recently developed and patented SHEFROL® bioreactors. The plants were utilized in a unit of capacity 12,000 liters/day (LPD) which, after two years of use, was enlarged to handle 40,000 LPD of sewage. It was then further expanded after an year to treat 57,000 LPD. All the five weeds, of which none has previously been tested in a pilot-scale SHEFROL, were able to foster highly efficient primary treatment (in terms of suspended and total solids) and secondary treatment (in terms of BOD and COD) to levels exceeding 85% in most cases. Additionally, the weeds also helped in achieving significant tertiary treatment. At different hydraulic retention times, and at steady state, the five weeds achieved treatment of BOD, COD, suspended solids, nitrogen, phosphorous, copper, nickel, zinc, and manganese in the ranges, 80-95, 79-91, 82-95, 61-71, 51-73, 37-43, 30-38, 39-47, and 27-35%, respectively. It all occurred in a single process step and without the use of any machine or chemical. This made the system not only simple and inexpensive to install but also to maintain. Over continuous long-term operation for four years, the system was seen to be very robust as it was able to handle wide variations in the volumes and characteristics of sewage, as well as absorb shock loads without compromising the reactor performance. The sustainability of the system can be further enhanced by upgrading it to a circular biorefinery. Energy sources in the form of volatile fatty acids (VFAs) can be extracted from the weeds removed from SHEFROL and then the weeds can be converted into organic fertilizer using high-rate vermireactors recently developed by the authors.