Study of the performance of a filter medium consisting of a layer of hemp shives on a layer of olive pomace in the treatment of domestic wastewater: scale-up from biofiltration pilot to full-scale
Two agro-industrial by-products were studied in biofiltration of domestic wastewater at pilot scale: hemp shives working as “active layer”, or top layer, on olive pomace working as “support layer”, or bottom layer. The aim of this work was to study the treatment capacity of these two materials working together as one single porous filter medium. The first biofilter had an equal proportion of both materials while the second one had 80% of the active layer and 20% of the support layer. The objective was to study the impact of the layer height on the biofilter performance. Both pilots were fed with synthetic sludge-based wastewater at a rate of 75 L·d‐1·PE‐1 (PE: population equivalent). Results showed a reduction of more than 90% of the biochemical oxygen demand at five days (BOD5) and the total suspended solids (TSS) after ten weeks of continuous operation. The performance remains good after more than 30 weeks of operation. Since the laboratory results were very encouraging, six prototype biofilters were installed to treat domestic wastewater from single-family residences under real conditions. The short-term purposes of this study are to determine the maintenance required by such a novel technology and to study the influence of parameters such as filter height, aeration, and the number of inhabitants. While the long-term goal is to characterize the treatment efficiency of these prototypes over many years under field conditions. The long-term treatment efficiency of one of the biofilters, which has been running for almost four years, is outstanding. The mean reduction in the chemical oxygen demand (COD), BOD5, and TSS is over 83%, 97%, and 96% respectively, rising expectations for the other five prototypes.