Study of Biological Treatment of Rice Mill Wastewater Using Anaerobic Semicontinuous Reactors (ASCR)

Anaerobic digestion (AD) of industrial wastewater has drawn researchers’ attention due to biofuel’s recovery in the form of biomethane. This study introduced two anaerobic semi-continuous reactors (ASCR)- R1 and R2 for bioremediation of the rice mill wastewater (RMWW). The alkali treatment of the substrate in reactors R1 and R2 was done by dry NaOH and Ca(OH)2, respectively. Both reactors were loaded with 80% of the RMWW and 20% of the cow-dung-fed biogas plant sludge (BGPS) for 16 days of stabilization at mesophilic temperatures (18℃ to 42℃). A small amount of jaggery and white rot fungi (Phanerochaete chrysosporium) were also added into both reactors for the bacterial growth and removal of the biorefractory organics (lignin and phenol) present in RMWW, respectively. The impact of variations in the hydraulic retention time (HRT) and organic loading rate (OLR) upon the anaerobic biodegradation of RMWW was studied in three operating phases (OP) I, II, and III. The highest BOD, COD, lignin, and phenol removal achieved in reactors R1 and R2 were 94%, 92%, 84%, and 82%, as well as 93%, 91%, 82%, and 80%, respectively, in OP I. The highest biomethane yield in both reactors was 0.005 L.g-1 COD in OP II. The results of the three operating phases reveal that a high HRT and low OLR give the maximum pollutant removal efficiency and the highest biomethane yield. The novelty of this research paper is the significant removal of the biorefractory organics lignin and phenol from the RMWW with the help of white rot fungi and specific bacterial strains Bacillus sp., Pseudomonas sp., Enterobacter sp., Actinomycetes sp. and Streptomycetes sp. present in the inoculum. The digestates from reactors were rich in macro and micronutrients viz., N, P, K, Cu, Zn, Fe, etc., essential for plant growth.