Sequential valorisation of microalgae biomass grown in pig manure treatment photobioreactors

Bioenergy production from swine wastewater based on a combined process of anaerobic dynamic membrane reactor and microalgae cultivation: Feasibility and performance

Enhanced methane production and sustainable reduction of pollutants from anaerobic digestate are crucial for swine wastewater treatment. In this study, anaerobic dynamic membrane bioreactor (AnDMBR) was introduced to enhance methane production, then microalgae were cultivated on the digestate for nutrients recovery and lipid production. Results showed that pollutants can be effectively removed under various hydraulic retention time (HRT) conditions during long-term operation. Methanogenesis was enhanced with the reduction of HRT from 20 days to 10 days (0.23 L-CH4/g-CODremoved), but inhibited by shortening HRT to 5 days (0.09 L-CH4/g-CODremoved). Ammonia and phosphate in the digestate were effectively removed after microalgae cultivation. In addition, the highest microalgal biomass and lipid productivity (1.7 g/L and 17.5 mg/(L·d), respectively) were obtained using digestate ratio of 20 %, while microalgal growth was seriously restricted at high digestate content (>50 %). This work provides a prospective pathway for pollutants control and energy production from swine wastewater through integrating of AnDMBR technology with microalgae cultivation.

Annual assessment of the wastewater treatment capacity of the microalga Scenedesmus almeriensis and optimisation of operational conditions

The depth of the culture and the dilution rate have a striking effect on the biomass productivity and the nutrient recovery capacity of microalgal cultures. The combination of culture depth and dilution rate that allows to maximise the performance of the system depends on environmental conditions. In the current study, a response surface methodology was used to explore the relationship between the two most relevant operational conditions and the biomass productivity achieved in 8.3 m² pilot-scale raceways operated using urban wastewater. Four polynomial models were developed, one for each season of the year. The software predicted biomass productivities of 12.3, 25.6, 32.7, and 18.9 g·m^-2·day^-1 in winter, spring, summer, and autumn, respectively. The models were further validated at pilot-scale with R² values ranging within 0.81 and 0.91, depending on the season. Lower culture depths had the advantage of minimising nitrification and stripping but allow to process a lower volume of wastewater per surface area. Biomass productivity was higher at culture depths of 0.05 m, when compared to 0.12 and 0.20 m, while the optimal dilution rate was season-dependent. Results reported herein are useful for optimising the biomass productivity of raceway reactors located outdoors throughout the year.

Second-Generation Phosphorus: Recovery from Wastes towards the Sustainability of Production Chains

Phosphorus (P) is essential for life and has a fundamental role in industry and the world food production system. The present work describes different technologies adopted for what is called the second-generation P recovery framework, that encompass the P obtained from residues and wastes. The second-generation P has a high potential to substitute the first-generation P comprising that originally mined from rock phosphates for agricultural production. Several physical, chemical, and biological processes are available for use in second-generation P recovery. They include both concentrating and recovery technologies: (1) chemical extraction using magnesium and calcium precipitating compounds yielding struvite, newberyite and calcium phosphates; (2) thermal treatments like combustion, hydrothermal carbonization, and pyrolysis; (3) nanofiltration and ion exchange methods; (4) electrochemical processes; and (5) biological processes such as composting, algae uptake, and phosphate accumulating microorganisms (PAOs). However, the best technology to use depends on the characteristic of the waste, the purpose of the process, the cost, and the availability of land. The exhaustion of deposits (economic problem) and the accumulation of P (environmental problem) are the main drivers to incentivize the P’s recovery from various wastes. Besides promoting the resource’s safety, the recovery of P introduces the residues as raw materials, closing the productive systems loop and reducing their environmental damage.