Experimental study on the biotreatability of wastewaters from food processing industries in aerobic sequencing batch reactors

The study was carried out to assess the effectiveness and limitations of aerobic biological treatment for the removal of organic matter from the food industry wastewaters. Four wastewaters from the UK food and drink industry were treated using an aerobic biological process carried out in lab-scale sequencing batch reactors (SBRs). Each reactor was inoculated with soil and monitored for chemical oxygen demand (COD) and total suspended solids (TSS) removal. The results showed high COD removal efficiencies for all the wastewaters, in the range of 64 – 95 %. The removal of TSS was different for the four wastewaters, and was not satisfactory. The food to microorganism (F/M) ratio calculated in all the reactors was quite low (0.13 - 0.29 kg COD/kg biomass.day) which contributed to the incomplete COD removal and poor TSS removal. In spite of the same cycle pattern, hydraulic retention time and length of the phases, the results indicate that solids removal is mainly determined by the nature and size of the particulate matter, rather than the process conditions. The residual soluble COD in the effluent was not further biodegradable, as indicated by extended aeration tests. The performance of the reactors was virtually unaffected by the solids retention time (SRT) (in the range investigated, 7 – 18 days), indicating that very good COD removal can be achieved at relatively lower SRT, with potential savings in capital and operating costs.