The effect of algal biomass on the removal of faecal coliform from domestic wastewater

The effect of algal density on faecal coliform (FC) decay under conditions of light and darkness were monitored in low and medium strength wastewater and in a ‘mixture of treated and raw wastewater’ depicting conditions of a variety of dissolved organic compounds. Rates of decay of FC varied in darkness with varying chlorophyll-a concentrations, supporting the hypothesis that algae may produce substances that are toxic to FC. The first empirical evidence that an optimum chlorophyll-a concentration (10 ± 2 mg L −1 ) for maximum FC destruction in wastewater exist is reported. Rate of decay was higher in medium strength wastewater compared with low strength wastewater at higher algal densities of ≥13.9 mg L −1 chlorophyll-a both in light and in darkness, while addition of fresh wastewater to an ongoing wastewater treatment process may lower the rate of FC decay for a wide range of algal densities (0.6–19.6 mg L −1 ), under light conditions.