Batch coagulation of a lagoon for fecal coliform reductions

The research examined the factors affecting fecal coliform removal from lagoon wastewater by batch treatment with aluminum sulphate. Laboratory experiments based on factorial designs and jar test were used to determine the statistically significant factors controlling the removal of fecal coliform bacteria. Temperature, chemical dose, pH, rapid mixing and flocculation were examined at two different laboratory scales. The results indicated that alum dose and pH were the only significant parameters. A design chart was developed for the wastewater tested enabling dose determination for a desired fecal coliform reduction. This chart was used to select the dose for a full scale field trial to reduce fecal coliforms to <10 per 100 ml. The design dose was 300 mg l-1 Al2(SO4)3·18 H2O and a final pH of 6.4 was predicted. The field trial used liquid alum (Al2(SO4)3·14.2 H2O) delivered by tanker truck and distributed by motor boat. The treatment reduced fecal coliforms by 99.9%, total phosphorus by 97%, total suspended solids (TSS) by 90% and 5-day carbonaceous biochemical oxygen demand (CBOD5) by 35%. The cost of treatment for labour and materials was $CDN 0.07 m-3.