Treatment and Re-Use of Raw Blackwater by Chlorella vulgaris-Based System

Abstract

In this study, we examined a Chlorella vulgaris-based system as a potential solution to change liquid waste, such as blackwater, into valuable products for agriculture while protecting waters from pollution without technical demanding pre-treatment. To evaluate the possibility of nutrient removal and biomass production from raw blackwater, four blackwater dilutions were tested at lab-scale: 50%, 30%, 20%, and 10%. The results showed that even the less diluted raw blackwater was a suitable growth medium for microalgae C. vulgaris. As expected, the optimum conditions were observed in 10% blackwater with the highest growth rate (0.265 d−1) and a nutrient removal efficiency of 99.6% for ammonium and 33.7% for phosphate. However, the highest biomass productivity (5.581 mg chlorophyll-a L−1 d−1) and total biomass (332.82 mg dry weight L−1) were achieved in 50% blackwater together with the highest chemical oxygen demand removal (81%) as a result of the highest nutrient content and thus prolonged growth phase. The results suggested that the dilution factor of 0.5 followed by microalgae cultivation with a hydraulic retention time of 14 days could offer the highest biomass production for the potential use in agriculture and, in parallel, a way to treat raw blackwater from source-separation sanitation systems.

Elimination of Vibrio Cholerae from Raw Sewage Using Chlorella Vulgaris: A Case of Chegutu Waste Reticulation, Zimbabwe

“…Increased salinity in sewage wastewater results in decreased DO because saltier water holds less oxygen. In this study, salinity decreased by 100% from 5 ppt to 0 ppt thereby conforming to findings by (Segovia-Bifarini et al, 2020).…”

“…TSS value is generally increased by the presence of organic and inorganic matter in sewage (Wang et al, 2010). The 64.5% reduction was therefore as a result of utilization of the organic and inorganic compounds (Segovia-Bifarini et al, 2020). In another study by Kumar et al (2013), Chlorella vulgaris reduced TDS by 97.5%.…”

“…Cooper and Smith (2015) explain that as the pH increases, the DO also increases and they attribute this increase to microalgal photosynthesis which produces oxygen molecules. Another study by Segovia-Bifarini et al (2020) revealed that DO is affected by salinity. Increased salinity in sewage wastewater results in decreased DO because saltier water holds less oxygen.…”

“…This could have been caused by the elevated pH which affects nitrate assimilation. Segovia-Bifarini et al (2020) explain that ammonium is a form of nitrogen preferred by microalgae because very little energy is used in ammonium assimilation as compared to nitrates. However, in pH above 8, the ammonium disintegrates to form ammonia, a form of nitrogen toxic to microalgae.…”

Nature-Based Units as Building Blocks for Resource Recovery Systems in Cities

“…However, the optimum range of pH and dissolved organic carbon can be regulated by the injection of CO 2 , enhancing algal production, promoting aggregation and bio-flocculation of algae with bacterial flocs to further enhance algal settling [55] and nitrogen removal by providing the necessary carbon to stimulate algal growth and reduce pH [56]. In PBRs, optimal conditions for microalgae growth should be maintained to achieve maximum efficiency of the system including vital algae inoculum, sufficient light availability for algae growth, hydraulic retention times (up to 20 days), and the surface area needed for algae ponds (20 g dry weight m −2 d −1 ), while avoiding contamination by fungi and zooplankton [57][58][59].…”