Alternative filtration media for wastewater : A dissertation submitted in partial fulfilment of the requirements for the Post Graduate Diploma of Agricultural Science at Lincoln University

Abstract

Eight columns lightly packed with four alternative media types were monitored to determine the treatment capacities. Alternative media types and quantities utilised included: 30 cm Sphagnum peat, 30 cm bark chips, 30 cm coffee hulls and 14 cm sand. Each column was dosed twice a day with septic tank effluent (STE) at 40 mm/day hydraulic loading rate (0.7 litres/day). Chemical oxygen demand (COD) was reduced by 59% in sand, 36% in peat, 20% in bark chips and 3 to 5 times more COD was observed in coffee hull. Removal of suspended solids (SS) by peat filter was 40 %, sand filter by 20% and bark filter indicated an addition of SS load by 0.09 mg/l to the STE. Reduction of coliform forming units (CFU) were obtained by all alternative media types, except coffee hull. Ninety one percent reduction was achieved by sand, 73% by peat and 66% by bark filter. These results indicate the suitability of peat, bark chips and sand as alternative treatment mediums for STE. Total solids for the column effluent (CE) from peat and sand showed no difference from the STE of 0.38 mg/l, indicating that there was no reduction. Bark chips had a slight increase (0.69 mg/l) from the STE. Colour from the column effluent appeared to be interferring with phosphorus (P) and nitrogen (N) analyses. After adding carbon (to remove colour) and then centrifuging the effluent, 43% P reduction in bark chips and 94% in sand was achieved. The corresponding reductions of 71 % for bark and 88% for sand were attained after filtering the CE. Increase in nitrate-nitrogen from all samples and repeats were recorded. Addition or subtraction of P, N and other substances to the column effluent by adding carbon, centrifuging and filtering processes is uncertain and is contrary to the objective of this study.