Shiqing Sun

Different gradient concentrations of vitamin B12 (0, 10, 100, 1,000 ng L⁻¹) were used in the symbiosis system (Chlorella vulgaris–Ganoderma lucidum or Chlorella vulgaris–Pleurotus ostreatus) to assess their effect on simultaneous purification of biogas and removal of nutrients in biogas slurry using co‐culture of microalgae and fungi. When B12 was added to the symbiosis system, biomass growth, intracellular carbonic anhydrase activity (CA), chlorophyll a content (CHL‐a), photosynthetic characteristics of the two cultivation system, and removal efficiency of nutrients in biogas slurry and CO₂ in biogas were significantly higher than those in the control group. The optimal concentration of B12 was determined to be 100 ng L⁻¹ considering the removal efficiency of nutrients and CO₂. Maximum mean chemical oxygen demand (COD), total nitrogen (TN), total phosphorus (TP), and CO₂ removal efficiencies were 75.98 ± 6.26%, 78.46 ± 6.21%, 80.21 ± 6.83% and 61.08 ± 5.21% in Chlorella vulgaris–Ganoderma lucidum, respectively. This study showed the potential of microalgae and fungi symbiosis system with B12 addition for nutrient removal and biogas upgrading.Practitioner points: Vitamin B12 had positive effects on algal–fungal pellets growth. The optimal vitamin B12 concentration was 100 ng L⁻¹. The highest CO₂ remove rate was 61.08% by G. lucidum/C. vulgaris pellets. Vitamin B12 significantly improved photosynthetic performance of pellets.

Three microalgae‐based treatment technologies were applied for removing nutrients in piggery wastewater and CO₂ in biogas simultaneously. Chlorella vulgaris (C. vulgaris), Scenedesmus obliquus (S. obliquus), and Neochloris oleoabundans (N. oleoabundans) were selected for mono‐cultivation or co‐cultivation with fungi or activated sludge. The effects of initial inoculum concentration (low of 62.06 ± 6.23 mg/L, medium of 121 ± 9.34 mg/L, and high of 180 ± 12.78 mg/L) of microalgae/algal symbiont on the pollutant removal efficiency were evaluated. The results showed that cultivation of S. obliquus with activated sludge had a relatively high CO₂ and nutrients removal efficiency at a medium concentration of initial inoculum. The highest removal efficiency of total organic carbon, total nitrogen, and total phosphorus in piggery wastewater was 87.29%, 87.26%, and 90.17% by co‐cultivation of S. obliquus with activated sludge. The highest CO₂ removal of 64.28% could be achieved under co‐cultivation of S. obliquus and fungi at medium initial inoculum concentrations. This work will be helpful to promote the study of microalgae‐based biogas upgrading and piggery wastewater purification.Practitioner points: Nutrient and CO₂ were efficiently removed in moderate microalgal initial inoculum. Scenedesmus obliquus‐activated sludge cultivation achieved the highest nutrient removal. Co‐cultivation of S. obliquus and fungi showed the highest CO₂ removal. Zinc was removed efficiently in high microalgal initial inoculum. Chlorella vulgaris/S. obliquus‐activated sludge performed economically.

This study selected and tested five submerged aquatic vegetation‐based (SAV) wetlands to improve highway runoff treatment in best management practices. The removal efficiencies of suspended solid (SS), chemical oxygen demand (COD), total nitrogen (TN), ammonia nitrogen (), and total phosphorus (TP) in the five SAV wetlands were analyzed. Furthermore, the lead (Pb) and zinc (Zn) accumulation capabilities of five submerged macrophytes were determined. The obtained results show that Ceratophyllum demersum wetlands achieved the highest nutrient removal and had the heavy metal accumulation property. Vallisneria natans showed the highest bioaccumulation of Pb among all tested species. Ceratophyllum demersum wetlands showed the highest average removal efficiencies of SS (82.97%), COD (62.08%), TN (77.63%), (76.24%), TP (77.55%), Pb (96.24%), and Zn (91.23%). The tendencies of contaminant removal showed seasonal variation, and SAV wetlands performed better in summer than in spring and autumn. Consequently, SAV wetlands showed selectivity for contaminant removal.Practitioner points: Chemical oxygen demand (COD), total nitrogen (TN), and total phosphorus (TP) in highway runoff were removed by submerged aquatic vegetation (SAV). Ceratophyllum demersum and Myriophyllum spicatum wetlands performed well on heavy metal removing. Ceratophyllum demersum showed the highest removal efficiencies of TSS, COD, TN, , and TP. The SAV wetlands performed better in summer than in other seasons.

To investigate the effects of different microalgae and culture methods on the purification of domestic wastewater and biogas, Chlorella vulgaris and Scenedesmus obliquus were selected. Three different culture methods (monoculture, microalgal–fungi cocultivation, and microalgal‐activated sludge cocultivation) were used to remove nutrients from four different domestic wastewaters and remove CO₂ from raw biogas in a photobioreactor. The results show that the effluent from the centrate of pretreated urban wastewater (WW4) achieved the highest nutrient and CO₂ removal efficiency. Cocultivation of C. vulgaris and activated sludge achieved the highest COD, TP, and CO₂ removal efficiencies of 79.27%, 81.25%, and 60.39% with WW4, respectively. Cocultivation of C. vulgaris and fungi achieved the highest TN removal efficiency of 78.46% with WW4. The contents of C, N, and P in the microalgal‐activated sludge symbiont after treatment exceeded 50%, 8%, and 0.8%, respectively. Highly economically efficient energy consumption was achieved with WW4 for both C. vulgaris and S. obliquus. Microalgal‐activated sludge cocultivation was identified as the optimal option for the simultaneous purification of wastewater and biogas based on its high pollution and CO₂ removal efficiency. This provides a reference for the microalgal‐based purification of actual domestic wastewater and raw biogas.Practitioner points: Nutrient and CO₂ were efficiently removed by C. vulgaris with activated sludge. CO₂ was removed up to 60.4% and was economically viable. Cocultivation of C. vulgaris and fungi could achieve the highest TN removal with WW4.

BACKGROUND: This study aims to simultaneously reduce biogas slurry nutrient and upgrade biogas via microalgal production. Marine microalgae were grown in a culture medium containing a mixture of seawater and biogas slurry with CO₂ from synthetic biogas. The effects of different ratios of biogas slurry and various influent concentrations of CH₄ in synthetic biogas on the growth of Nannochloropsis sp. were examined. Nutrient removal and biogas upgrading were also studied under different influent CH₄ concentrations.RESULTS: Nannochloropsis sp. showed optimal growth in 40% biogas slurry and significantly enhanced growth in synthetic biogas with 50% CO₂. The optimal range of influent CH₄ concentration for the removal of biogas slurry nutrients was 45% to 50%. Notably, the influent CH₄ concentration of 60% (v/v) provided an optimal CO₂ concentration for Nannochloropsis sp. cultivation. Advantageous CO₂ removal and biogas upgrading were observed under this condition. This treatment increased CH₄ concentration in synthetic biogas from 60% to 93.58% after 6 days cultivation.CONCLUSION: Appropriate control of the biogas slurry or seawater and CH₄ concentrations in the influent is crucial to simultaneously optimize nutrient removal and biogas upgrading. © 2015 Society of Chemical Industry