Influencing factors for nutrient removal from piggery digestate by coupling microalgae and electric field.

Microalgae show great potential for nutrient removal from piggery digestate. However, full-strength piggery digestate have been found to severely inhibit microalgal growth. In this study, microalgae were coupled into the electric field (EF)system to form an electric field-microalgae system (EFMS). The effects of EF characteristics and environmental conditions on the growth of Desmodesmus sp. CHX1 and the removal of nitrogen and phosphorus in EFMS were explored. The results indicated that the optimal EF parameters for forming a fine EFMS were electrode of Zn (anode)/graphite (cathode), electric frequency of three times per day (10 min/time) and voltage of 12 V. The suitable light intensity and microalgae inoculation concentration for the EFMS were 180 µmol photons/(m2·s) and 0.2 g/L, respectively. Ammonium nitrogen and total phosphorus removal efficiencies were 65.38% and 96.16% in the piggery digestate by EFMS under optimal conditions. These results indicate that EFMS is a promising technology for nutrient removal from piggery digestate.

Effect of Microplastics on the Removal of Nitrogen and Phosphorus from Synthetic Piggery Digestate by Microalgae.

Microplastics (MPs) have been proven to be one of the major threats to the wastewater treatment system. However, the impact of MPs on microalgae-based wastewater treatment technology are still unknown. In this study, effects of polyvinyl chloride (PVC), polypropylene (PP), and polyethylene (PE) on the removal of nitrogen and phosphorus from synthetic piggery digestate by microalgae were investigated. Results show that the effect of PVC particle size on the growth of microalgae was significant. The effects of PVC content, PP particle size and content, PET particle size and content on the growth of microalgae were all not significant. The removal of ammonia nitrogen by microalgae was influenced significantly by PVC particle size and content, PP particle size and content, the effects of PET particle size and content on the removal of ammonia nitrogen were all not significant. The effects of particle size and content for three MPs on the removal of total phosphorus were all significant. Microalgae cells were bound together after being adsorbed by MPs, which increased the secretion of extracellular polymers and influenced the removal of ammonia nitrogen and total phosphorus.

Enhanced removal of humic acid from piggery digestate by combined microalgae and electric field.

Microalgae technology is a promising method for treating piggery digestate, while its removal ability of humic acids (HAs) is poor. Here, an electric field-microalgae system (EFMS) was used to improve the removal of HAs from the piggery digestate. Results indicated that the removal of HAs by EFMS relied on the initial concentration of HAs, electrical intensity, the initial inoculation concentration of microalgae and pH. Values of these parameters were optimized as electrical intensity of 1.2 V/cm, microalgae initial inoculation concentration of 0.1 g/L and pH 5.0. The HAs removal efficiency by EFMS (55.38%) was 13% and 38% higher than that by single electric field and microalgal technology. It was observed that oxidation, coagulation and assimilation contributed to the removal of HAs, suggesting that EFMS could serve as an attractive and cost-effective technique for the removal of HAs from the piggery digestate.

Response surface methodology to optimize self-flocculation harvesting of microalgae Desmodesmus sp.CHX1.

This study aims to optimize the self-flocculation ability of microalgae Desmodesmus sp. CHX1 by the response surface methodology (RSM). Key parameters (i.e. pH, temperature and flocculation time) that significantly affected the Desmodesmus sp.CHX1 flocculation were determined. Results show that the flocculation efficiency of Desmodesmus sp.CHX1 increased in response to the prolonged settling time, particularly within the first 6 h, given the secretion of extracellular polymers. The RSM result suggested that both temperature and time exerted more significant effects on flocculation efficiency than solution pH. In specific, the maximum flocculation efficiency could reach 94.0% under the optimal conditions with the temperature, time and pH of 12.37°C, 6.96 h and 7.98, respectively. Validation experiments further indicated the reliability of the optimal parameter conditions.

Effect of nano-TiO2 on humic acid utilization from piggery biogas slurry by microalgae.

Resource recovery from piggery biogas slurry has become an inevitable demand for sustainable development of pig industry. Microalgae show great potential in recovering nitrogen and phosphorus from piggery slurry, but struggle to utilize organic pollutants, as most of them are inert components (e.g., humic acids, HAs). In this study, nano-TiO2 was used to enhance the utilization of HAs by microalgae from piggery biogas slurry. Results showed that the optimal conditions for microalgal growth and HAs removal by the microalgae-TiO2 coupling system were TiO2 dosage of 0.30 g/L, microalgal inoculation concentration of 0.40 g/L, light intensity of 360 µmol photon/(m2·s) and temperature of 30 °C, with the microalgal chlorophyll concentration of 6.51 mg/L and HAs removal efficiency of 50.14%. Analysis of HAs composition variations in the piggery biogas slurry indicated that the decrease of HAs was caused by their decomposition into small molecules under the photocatalytic reactions of TiO2.

Performance of a novel photobioreactor for nutrient removal from piggery biogas slurry: Operation parameters, microbial diversity and nutrient recovery potential.

Photobioreactor is deemed to be one of limiting factors for the commercial application of wastewater treatment based on microalgae cultivation. In this study, a novel Flat-Plate Continuous Open Photobioreactor (FPCO-PBR) was developed to treat piggery biogas slurry. The operation parameters, microbial stability and nutrient recovery potential of FPCO-PBR were investigated. Results showed that the appropriate influent mode for FPCO-PBR was multi-point or spraying mode. The optimal hydraulic retention time and interval time for biomass harvesting of FPCO-PBR were both 2 d. Nitrogen and phosphorus recovery rate were 30 mg L-1 d-1 and 7 mg L-1 d-1 respectively under optimal operating parameters. Microbial diversity remained relatively stable in FPCO-PBR. Biomass production rate of FPCO-PBR was 0.47 g L-1 d-1 under optimal operating parameters. The revenue generated from biomass was estimated to be 15.06 $ kg-1, which means that treating one ton of wastewater can generate $ 7.08 in revenue.