Rice parboiling and dairy processing industries are among emerging and lucrative food processing industries in Sri Lanka in terms of production, consumption and export prospects. Compared to other industries, food processing industry is heavily dependent on freshwater with potable water quality standard. However, wastewater generated from food processing industries are among the costly waste to treat as they contain large quantities of nutrients, organics,  inorganics, suspended solids and dissolved solids. In Sri Lanka, rice parboiling and dairy processing industries are categorized under medium, small, micro enterprises category, thus most of these enterprises cannot afford the cost of conventional activated sludge based wastewater treatment technologies. Consequently, wastewater generated from most of food processing industries are released in to the environment without any treatment.

Recent advances in microalgae biotechnologies have provided promising solutions for municipal wastewater treatment.  Microalgae have the ability to assimilate Nitrogen, Phosphorus and minor nutrients while the microalgae biomass can be converted to value added products such as   biofuels, animal feed, fertilizer and constituents in pharmaceutical and cosmetic industry and as potential biofuel. However, there is some considerable controversy surrounding the bioaccumulation of heavy metals and other micro pollutants by microalgae in municipal wastewater medium. This scenario can limit the end use of microalgae biomass into useful products such as animal feed or biofertilizer.  This study aimed to provide a cost effective solution for the treatment of parboiled rice mill and dairy wastewater using microalgae and convert the microalgae biomass into biofertilizer.

A green microalga, Chlorella sp was isolated from polluted lakes and grown under laboratory conditions to provide seed cultures for cultivation of microalgae in laboratory-scale bioreactors.  Microalgae were cultivated in 2L-polybags and 150L-raceway reactors at indoor and outdoor conditions.   Both parboiled rice mill and dairy wastewater samples were collected in Kilinochchi area. The average removal efficiency of total nitrogen in the parboiled rice mill and dairy wastewater was 88% and 99%, respectively. The removal efficiency of the phosphate in both wastewaters ranged between 75-76%. The reduction of COD (chemical oxygen demand) in dairy wastewater was about 90% while maximum of 87% COD removal was observed with parboiled rice mill wastewater. The harvested microalgae biomass exhibited 36% (w/w), 19% (w/w), 6% (w/w) of total nitrogen, total phosphorous and total potassium respectively confirmed its potential use as bio-fertilizer.  Thus, the present study demonstrated the use of microalgae for the treatment of dairy wastewater and parboiled rice mill wastewater while confirming the viable use of microalgae biomass for biofertilizer production.

Key words: Microalgae, dairy wastewater, ricemill wastewater, biofertilizer