Wastewater nutrient recovery using twin-layer microalgae technology for biofertilizer production

This study evaluates the feasibility of advanced biofilm microalgae cultivation in a twin layer (TL) system for nutrient removal (N and P) as the tertiary treatment in small wastewater treatment plants (WWTPs) located in sensitive areas. Furthermore, the potential valorisation of microalgae biomass as a component of bio-based fertilizers is assessed. Scenedesmus sp. was chosen among 33 microalgae strains for inoculation of TL due to its high growth rate and its nutrient uptake capacity. The tests carried out in the prototype were markedly efficient for total soluble and ammoniacal nitrogen removal (up to 66 and 94%, respectively). In terms of potential valorisation of microalgae, the nutrient content was 5.5% N (over 40% protein), 8.8% P2O5 and 1.5% K2O, high enzymatic activity, very low levels of heavy metals and no detectable pathogen presence. However, in the formulation of solid-state bio-based fertilizers, the microalgae proportions in blends of over 2% of microalgae led to negative effects on ryegrass (Lolium perenne L. ssp.) and barley (Hordeum vulgare ssp.). The obtained results demonstrate that TL represents a promising technology, which allows efficient tertiary treatment of urban wastewater and the production of high-quality bio-based fertilizer.

Economic and environmental impact analysis of ammoniacal nitrogen removal from landfill leachate using sequencing batch reactor: a case study from Czech Republic

Lany landfill, located in the Czech Republic, generates around 10 m3/d of leachate, heavily polluted with ammoniacal nitrogen, heavy metals and salts, which needs to be treated onsite in order to minimize their effect on the ecosystem and on human health. A sequencing batch reactor (SBR) was designed for ammoniacal nitrogen removal from the leachate and the economic feasibility and environmental impact of the designed SBR was assessed. From the cost-benefit analysis, capital expenditure (CAPEX) of 33,500 €/year and operational expenditure (OPEX) of 13,521 €/year were estimated. A shadow price concept tool was used to calculate the environmental benefit as 21,000 €/year. The net present value of the project was evaluated to be 19,528 € with an internal rate of return of 21.6%. For environmental assessment, triple bottom line (TBL) analysis on the existing practice of discharging the leachate to a nearby wastewater treatment plant and on-site treatment using SBR was performed. The total score for existing practice was calculated to be 55.1% while for on-site treatment it was 59.6%. Based on the results it was concluded that on-site treatment is both economically and environmentally feasible. A mitigation plan was also prepared for the impacts identified in the environmental assessment.