Environmental Conditions and Enterococci Removal in Macrophyte and Algal-Based Domestic Wastewater Treatment Systems

The environmental conditions and faecal enterococci removal in batch-scale water lettuce ( Pistia stratiotes), duckweed ( Lemna paucicostata ) and algal ponds were determined over a period of 29 days under tropical conditions. Batch-scale incubation experiments were conducted in 4.5L plastic containers. A control of raw sewage stored under dark conditions was included. Environmental conditions such as temperature, pH, and DO, heterotrophic bacteria and enterococci populations were monitored four times a week at 8, 12 and 20 GMT. BOD and COD were monitored once a week for five weeks. Average temperatures within the systems ranged between 28.3°C in the raw wastewater to 30.6°C in the algal ponds. Low levels of pH 4.5 and DO levels of 3mg/L were recorded in the water lettuce ponds. The duckweed ponds had neutral pH and DO of 6mg/L. The raw wastewater under darkness had neutral pH and low DO concentrations. High pH levels around 10.5 and DO of about 20mg/L were observed in the algal ponds in the afternoons. All pond systems performed equally well in enterococci removal and BOD reduction. The enterococci population decreased from 1.2 x10 4 /100mL to values < 100/100mL in all treatment systems. The BOD decreased from 130mg/L to 5.0, 7.5, 10 and 15mg/L in the duckweed, water lettuce, raw wastewater and algal treatment systems respectively.