EFFECTIVENESS OF HORIZONTAL ROUGHING FILTER COMBINED WITH SELECTED ALGAE SPECIES ON QUALITY OF GREYWATER AND PRODUCTION OF USEFUL BIOMASS

Abstract

Discharging greywater into open ground remains a major management practice usually causing surface water pollution and exposure of people to water-related diseases particularly in low to middle income communities. Studies have shown that treatment of greywater with Horizontal Roughing Filter (HRF), a primary treatment process for wastewater, combined with algae species (sp.) has not been adequately utilized in Nigeria. However, cultivating algae on HRF-treated greywater may reduce surface water pollution, water-related diseases and produce useful biomass than opting for open discharge. Therefore, this study evaluated the effectiveness of Chlorella sp. combined with HRF (CHRF) and Scenedesmus sp. combined with HRF (SHRF) in greywater treatment and production of useful biomass.

Greywater was sourced from households in Kube-Atenda community, Ibadan North Local Government Area, and subjected to CHRF and SHRF treatments while untreated sample served as control. Cultures of the algae species (Chlorella sp. and Scenedesmus sp.) were isolated from a fish pond in Ibadan and identified by their morphological characteristics. Growth conditions of the Chlorella sp. and Scenedesmus sp. were optimised in the laboratory and an outdoor experiment was conducted in a fabricated 100L capacity batch type treatment unit. Greywater (75L) was used with Chlorella sp. and Scenedesmus sp. inoculation dose of 20% for 12 days (a batch) over a period of 3 months (6 batches) for each of CHRF and SHRF treatments. Samples from each of the treatments and control were analysed for pH, Biochemical Oxygen Demand (BOD), nitrate, phosphate and Total Coliform (TC) using standard methods. Algae samples were analysed for chlorophyll-a, growth rate, crude protein and dry weight. Laboratory analyses were replicated three times and greywater quality results were compared with National Environmental Standards and Regulations Enforcement Agency (NESREA) quality standard. Data were analysed using descriptive statistics, t-test and ANOVA at α0.05.

The pH of treated greywater were 9.1±0.6 (CHRF), 8.8±0.5 (SHRF) and 6.6±0.5 (control). The BOD (mg/L) reduced significantly from 125.7±6.4 (control), to 43.4±2.2 (CHRF) and 42.5±2.1 (SHRF), corresponding to 65.5% (CHRF) and 66.3% (SHRF) reduction. Nitrate concentration (mg/L) of the control, 42.1±2.9 significantly reduced to 11.6±0.8 (CHRF) and 10.4±0.7 (SHRF). Nitrate values of CHRF and SHRF were within the recommended limits (10-15 mg/L). Phosphate concentration (mg/L) reduced significantly from 16.8±3.9 (control) to 4.3±2.3 (CHRF) and 3.4±2.1 (SHRF). The TC count (MPN/100mL) of the control (8.3±2.1)x103 significantly reduced to (9.0±0.14)x102 and (7.8±0.12)x102, respectively, for CHRF and SHRF treated sample. The TC values of CHRF and SHRF were within the recommended limits (<103 MPN/100mL). Chlorophyll-a value was 3.8±2.7 mg/L (Chlorella sp.) and 4.2±2.8 mg/L (Scenedesmus sp.) with growth rate of 2.37 g/day (chlorella sp.) and 1.83 g/day (Scenedesmus sp.) Protein content (%) of Scenedesmus sp. 14.6±1.8 was significantly higher compared to 12.7±1.4 for Chlorella sp. while dry weight was 612.9±93.1 g (Scenedesmus sp.) and 576.2±95.7 g (Chlorella sp.).

The Horizontal Roughing Filter in combination with algae was effective in treating greywater, and Scenedesmus species produced biomass with higher protein content and dry weight. This technology could be used in treating greywater and cultivate beneficial algae at the household level where wastewater treatment facilities are lacking.