Abstract:
The necessity for natural or biological fertilizers instead of synthetic fertilizers arises from
the growing demand for food and awareness of environmental pollution due to inorganic
fertilizers. In order to increase crop productivity and create healthy plants, microalgae have
emerged as a potential source of bio stimulants and biofertilizers in agriculture. Chlorella
sp. has been identified as a potential bio-fertilizer. This study investigated the formulation
of a liquid organic fertilizer (LOF) by using Chlorella sp. grown in dairy industry wastewater
according to the Sri Lanka Standards Institution (SLSI) standards for LOF. The Chlorella
sp. was cultivated in dairy waste water in a raceway reactor for 14 days continuously with
constant light intensity and constant mixing to optimize the algal growth. The nutrient
content of dry biomass of Chlorella sp. grown in dairy industry effluent was 5% nitrogen,
2.33% phosphorous and 2.68% potassium. The nutrient content of formulated Chlorella
liquid organic fertilizer was 1% nitrogen (N), 0.58% phosphorous (P) and 0.67% potassium
(K). pH and EC were 7.4 and 9.8 ds/m respectively. The trace metal content in the formulated
LOF was 0.0047 ppm chromium (Cr) and 0.0023 ppm arsenic (As). Cadmium (Cd) and lead
(Pb) were not detected. According to SLSI standards, the LOF should contain 6.0 – 8.5 pH,
20.0 ds/m EC (maximum), 1% total nitrogen, 0.5% total phosphorous, 0.5% total potassium
in minimum, and 0.5 ppm chromium. Also, heavy metal concentration of LOF should be 0.5
ppm arsenic, 0.5 ppm cadmium and 1.0 ppm lead in maximum concentration. The
formulated LOF using Chlorella sp. grown in dairy wastewater fulfilled the chemical
requirements and trace metal requirements of SLSI recommendations. This study highlights
the feasibility of formulating a liquid organic fertilizer using Chlorella sp. cultivated in dairy
wastewater, aligning with the requirements outlined by SLSI standards.
