Growth kinetics of microalgae cultivated in different dilutions of fresh leachate for sustainable nutrient recovery and carbon fixation

Effect of hydrothermal pretreatment on leachate fed Scenedesmus sp. biomass solubilization and biogas production

The aim of the present study was to assess the effect of hydrothermal pretreatment on the solubilization and anaerobic digestion (AD) of Scenedesmus sp. biomass. At first, the microalgae was cultivated in 5% fresh leachate (FL) to recover nutrients such as nitrogen and phosphorus. Scenedesmus sp. grown in 5% FL obtained 100%, 77% and 97% removal efficiency of ammonium nitrogen (NH4+ - N), total Kjeldahl nitrogen (TKN) and phosphate phosphorous (PO43- -P), respectively. In the following step, the hydrothermal pretreatment of Scenedesmus sp. biomass was carried out at 120, 150 and 170 °C and retention time of 0, 30 and 60 min to evaluate its solubilization and biogas production through AD in batch test. Soluble chemical oxygen demand (sCOD) increased by 260% compared to untreated microalgae at 170 °C for 60 min. In comparison to untreated microalgae, the highest increase in biogas (70%) and methane yield (100%) was observed for 150 °C and 60 min pretreated microalgae as a consequence of hydrothermal pretreatment. Hydrothermal pretreatment has shown effectiveness in enhancing biomass solubilization and increasing biogas yield. Nevertheless, further research at the pilot scale is necessary to thoroughly evaluate the potential and feasibility of hydrothermal pretreatment for full-scale implementation.

Eco-friendly cultivation of microalgae using a horizontal twin layer system for treatment of real solid waste leachate

Solid waste leachate (SWL) requires dilution with water to offset the negative effects of high nutrient concentration and organic compounds for its microalgae-based treatment. Among attached cultivation systems, twin layer is a technology in which limited information is available on treatment of high strength wastewater using microalgae. Moreover, widespread application of twin layer technology is limited due to cost of substrate and source layer used. In the present study, potential of Scenedesmus sp. for the treatment of SWL was assessed on horizontal twin layer system (HTLS). Novel and cost-effective substrate layers were tested as attachment material. Wetland treated municipal wastewater (WMW) was used to prepare SWL dilutions viz, 5%, 10%, 15%, 20% and 25% SWL. Recycled printing paper showed maximum biomass productivity of 5.19 g m-2 d-1. Among all the SWL dilutions, Scenedesmus sp. achieved maximum growth of 103.05 g m-2 in 5% SWL which was 16% higher than WMW alone. The maximum removal rate of NH4+ -N, TKN, and PO43- P was obtained in 20% SWL which was 1371, 1588 and 153 mg m-2 d-1 respectively. Varying concentrations of nutrients in different SWL dilutions significantly affected lipid biosynthesis, with enhanced productivity of 2.28 g m-2 d-1 achieved in 5% SWL compared to 0.97 g m-2 d-1 in 20% SWL. Hence, it can be concluded that 5% SWL dilution was good for biomass and lipid production, while the highest nutrient removal rates were obtained at 20% SWL mainly attributed to biotic and abiotic processes. Based on these results HTLS can be a promising technology for pilot scale to explore industrialized application of wastewater treatment and algal production.

Potential application of a newly isolated microalga Desmodesmus sp. GXU-A4 for recycling Molasses vinasse

The development of cost-effective and energy-efficient technologies for the stabilization of organic wastewater by microalgae has been essential and sought after. In the current study, GXU-A4 was isolated from an aerobic tank treating molasses vinasse (MV) and identified as Desmodesmus sp. based on its morphology, rbcL, and ITS sequences. It exhibited good growth with a high lipid content and chemical oxygen demand (COD) when grown using MV and the anaerobic digestate of MV (ADMV) as the growth medium. Three distinct COD concentrations for wastewater were established. Accordingly, GXU-A4 removed more than 90% of the COD from molasses vinasse (MV1, MV2, and MV3) with initial COD concentrations of 1193 mgL^-1, 2100 mgL^-1, and 3180 mgL^-1, respectively. MV1 attained the highest COD and color removal rates of 92.48% and 64.63%, respectively, and accumulated 47.32% DW (dry weight) of lipids and 32.62% DW of carbohydrates, respectively. Moreover, GXU-A4 grew rapidly in anaerobic digestate of MV (ADMV1, ADMV2, and ADMV3) with initial COD concentrations of 1433 mgL^-1, 2567 mgL^-1, and 3293 mgL^-1, respectively. Under ADMV3 conditions, the highest biomass reached 13.81 g L^-1 and accumulated 27.43% DW of lipids and 38.70% DW of carbohydrates, respectively. Meanwhile, the removal rates of NH₄-N and chroma in ADMV3 reached 91.10% and 47.89%, respectively, significantly reducing the concentration of ammonia nitrogen and color in ADMV. Thus, the results demonstrate that GXU-A4 has a high fouling tolerance, a rapid growth rate in MV and ADMV, the ability to achieve biomass accumulation and nutrient removal from wastewater, and a high potential for MV recycling.

Nutrient recovery from municipal solid waste leachate in the scope of circular economy: Recent developments and future perspectives

Holistically considering the current situation of the commercial synthetic fertilizer (CSF) market, recent global developments, and future projection studies, dependency on CSFs in agricultural production born significant risks, especially to the food security of foreign-dependent countries. The foreign dependency of countries in terms of CSFs can be reduced by the concepts such as the circular economy and resource recovery. Recently, waste streams are considered as a source in order to produce recovery-based fertilizers (RBF). RBFs produced from different waste streams can be substituted with CSFs as input for agricultural applications. Municipal solid waste leachate (MSWL) is one of the waste streams that have a high potential for RBF production. Distribution of the published papers over the years shows that this potential was noticed by more researchers in the millennium. MSWL contains a remarkable amount of nitrogen and phosphorus which are the main nutrients required for agricultural production. These nutrients can be recovered with many different methods such as microalgae cultivation, chemical precipitation, ammonia stripping, membrane separation, etc. MSWL can be generated within the different phases of municipal solid waste (MSW) management. Although it is mainly composed of landfill leachate (LL), composting plant leachate (CPL), incineration plant leachate (IPL), and transfer station leachate (TSL) should be considered as potential sources to produce RBF. This study compiles studies conducted on MSWL from the perspective of nitrogen and phosphorus recovery. Moreover, recent developments and limitations of the subject were extensively discussed and future perspectives were introduced by considering the entire MSW management. Investigated studies in this review showed that the potential of MSWL to produce RBF is significant. The outcomes of this paper will serve the countries for ensuring their food security by implementing the resource recovery concept to produce RBF. Thus, the risks born with the recent global developments could be overcome in this way besides the positive environmental outcomes of resource recovery.

Insights into sustainable resource and energy recovery from leachate towards emission mitigation for environmental management: A critical approach

The exponential generation of municipal solid waste (MSW) and landfill disposal without any treatment has increased the continuous generation of landfill leachate. Improper MSW and leachate management are contributing to environmental degradation and water and soil pollution, which must be treated. Numerous works have been conducted on leachate treatments for energy and resource recovery. This review presents a comprehensive study of leachate management in which different treatment methods are discussed to analyze the suitability of processes that can be employed to treat leachate efficiently. Further, the characteristics of leachate are examined as properties of leachate may be varied depending upon the region. Still, several challenges related to leachate management and its treatments are discussed in this study. An integrated system could be a better option for treating leachate because it contains large amounts of organic and inorganic compounds. Proper leachate management would help to recover energy and value-added products (metals).

Nutrient removal and lipid production by the co-cultivation of Chlorella vulgaris and Scenedesmus dimorphus in landfill leachate diluted with recycled harvesting water

Applying microalgae for landfill leachate (LL) treatment is promising. However, LL usually needs to be diluted with much fresh water, aggravating water shortage. In this study, mono- and co-culturing microalgae (Chlorella vulgaris and Scenedesmus dimorphus) were used to treat LL diluted with recycled harvesting water, to investigate nutrient removal and lipid production. The results showed that microalgae in co-culture treatment had more biomass and stronger superoxide dismutase activity, which might be related to humic acids contained in recycled harvesting water, according to dissolved organic matters (DOMs) analysis. In addition, the lipid content and yield of co-cultured microalgae reached 27.60 % and 66.87 mg·L^-1, respectively, higher than those of mono-culture, proving the potential of co-culture for the improvement of lipid production. This study provided a freshwater-saving dilution method for LL treatment with recycled harvesting water as well as a strategy for the increase of biomass and lipid accumulation by microalgae co-cultivation.