The physico-chemical characteristics and amenability to biological treatment of sugar refinery effluent was evaluated by taking samples of the influent and effluent from the pretreatment plant of a sugar refinery plant. Manual and systematic sampling was used to collect the effluent samples and the effluent discharge was measured using an Millitronics open channel meter. Samples were analysed using standard methods as outlined in the Standard Methods Handbook (APHA, AWWA, WEF). The effluent was characterised by high concentrations of organic matter and low levels of pH, suspended solids (SS) and total dissolved solids (TDS). Chemical oxygen demand (COD) levels ranged from 755-22,780mgl-1 greatly exceeding the municipality regulatory limit of 2000mgl-1 in most instances, while the level of SS was well below the regulatory limit of 600mgl-1. The pH levels ranged from 5.1-8.4 and were below the lower regulatory control limit of 6.5 in most instances. The effluent was found to be readily biodegradable with a KL value of 0.71day-1 and therefore amenable to biological treatment process employed in the plant. However, the reduction in COD levels was initially less than 25% and after further refurbishments to the biological treatment plant a 50% reduction was achieved. The presence of biocides in the effluent from the cooling towers and lack of adequate bacterial slime in the trickling tower packing reduced the overall efficiency of the effluent treatment plant. The amount of effluent discharged per day ranged from 3-72m3 depending on production levels and approximately 10% of the total water used in the plant is discharged as effluent from the cooling towers and char house.
Key words: sugar refining, effluent characterization, biological treatment
