Shift of system performance and indicators of biofilm development in constructed wetland integrated with vermifilter treating synthetic rice mill wastewater

Abstract

Never been used in the remediation of rice mill wastewater (RMW), nature-based solutions, such as constructed wetland (CW) and vermifilter (VF), can be utilized to minimize the discharge of organic matter from the industry to the environment. This study employed a three-stage CW integrated with VF to treat synthetic RMW comprising recalcitrant and noxious pollutants such as lignin and phenol. Two systems were fed with synthetic RMW of COD 2000 mg/l with phenol and lignin concentrations of 10 mg/l and 150 mg/l (R1) and 20 mg/l and 150 mg/l (R2), respectively. The COD removal dropped from 92 ± 0.2 % in R1 to 82.2 ± 0.2 % in R2, and lignin from 78.4 ± 0.3 % in R1 to 74.4 ± 0.6 % in R2. The stimulation of proteins and polysaccharides in the bed media of the inlet section of R2 indicated the toxic impact of phenol, resulting in the increased synthesis of EPS as a protective shield for cells via a metabolic pathway. Biofilm batch assay revealed that the increased phenol concentration inhibited the growth of microbes, resulting in decreased biodegradation of COD from 42 ± 2 % in R1 to 29 ± 2 % in R2 and lignin from 28 ± 1.5 % in R1 to 23 ± 1.8 % in R2, respectively. This outcome was corroborated by the lesser population of heterotrophic bacteria, fungi, and actinomycetes in R2. Moreover, increasing phenol concentration reduced dehydrogenase and β-glucosidase enzyme activity by 27 % and 24 %, respectively. It also adversely affected the development of the Canna indica plant and resulted in mottling and wilting of leaves.