Cultivation of Scenedesmus dimorphus with domestic secondary effluent and energy evaluation for biodiesel production

From lab to application: Cultivating limnetic microalgae in seawater coupled with wastewater for biodiesel production on a pilot scale

The technology of cultivating salt-tolerant limnetic microalgae in seawater reduces the freshwater demand and costs of biodiesel production. However, all current trials still occur on the bench scale, and efforts for pilot-scale operation are urgently needed. This study firstly optimised the diameter of the photobioreactors (PBRs) to 0.2 m, as the single module to produce lipid-rich Golenkinia sp. SDEC-16 because of the better algal growth and light attenuation in the PBRs, and then established a 1000 L algal cultivation system. In a medium of seawater supplemented with monosodium glutamate wastewater at a ratio of 1:1000 (S-MSGW), the biomass productivity was 0.26 g/L/d, which was approaching the 0.30 g/L/d obtained in BG11, and the lipid productivity (98.99 mg/L/d) was doubled in comparison to growth in BG11. C16-C18 accounted for more than 98% of the total fatty acid in S-MSGW, and the biodiesel properties also met the biodiesel standards. The input cost of the biodiesel in this pilot-scale system was estimated to be 2.2 $/kg. When considering the carbon reduction and diversified application of the biomass, Golenkinia sp. would annually capture 186.77 kg/m³ PBR of CO₂, and yield an output-to-input ratio (OIR) of 3.4 in S-MSGW, higher than the 2.8 in BG11.

Advanced treatment of secondary effluent from wastewater treatment plant by a newly isolated microalga Desmodesmus sp. SNN1

Secondary effluents contain considerable amounts of nitrogen and phosphorous, which if dumped untreated can cause eutrophication of the receiving water bodies. Microalgae can remove these nutrients and other pollutants from the wastewater effluents and play an effective role in the secondary effluent treatment. In this study, six microalgae strains (SNN1, SNN2, SNN3, SNN4, SNS1, and SNS2) were isolated and screened from the water and mud of Yingxue Lake of Shandong Jianzhu University, and their efficiencies for the removal of COD, NH₄ ⁺-N, TN, and TP in the secondary effluent were assessed. By comparing the growth performances and nutrient removal ability of algal strains in domestic sewage, we found that SNN1 (identified and named as Desmodesmus sp. SNN1) has the highest efficiency for biomass accumulation and sewage purification. Hence, the algal strain SNN1 was selected for further screening and optimization experiments. The strain showed higher biomass yield and better nutrient removal rate when the pH of secondary effluent was 9.0 and the initial inoculum concentration (optical density at 680 nm) of algal strain was 0.4. After 12 days of treatment, the concentrations of COD, NH₄ ⁺-N, TN, and TP in the secondary effluent were 31.79, 0.008, 8.631, and 0.069 mg/L, respectively. Therefore, SNN1 with the removal rates of 52.69% (COD), 99.99% (NH₄ ⁺-N), 89.09% (TN), and 94.64% (TP) displayed its high potential in nutrient removal. In addition, it also yielded 5.30 mg/L of chlorophyll a and 168.33 mg/L of lipids. These results demonstrated that this strain exhibited an effective treatment capacity for secondary effluent and microalgal oil production. This study is helpful to provide a strategy for the resource utilization of secondary effluent and the conservation of freshwater resources required by microalgae culture.

Cultivating Scenedesmus dimorphus in lactic acid wastewater for cost-effective biodiesel production

The combination of lactic acid production wastewater and oil-producing microalgal culture could not only achieve harmless treatment of wastewater but also provided nutrients and significant amounts of water for microalgal culture. Thus the effects of different nutrients on the biomass yield, lipid yield of Scenedesmus dimorphus with lactic acid wastewater were investigated. Although lactic acid wastewater was very suitable for the cultivation of oil-producing microalgae, some nutrients were still needed. So 0.79 g/L NaNO₃, 14 mg/L MgSO₄·7H₂O, 4 mg/L K₂HPO₄·3H₂O, and trace elements needed to be added in the microalgal culture with lactic acid wastewater. In the optimized wastewater medium, the lipid yield could reach 1.54 ± 0.04 g/L, which was 48.1% higher than the level of 1.04 ± 0.06 g/L in the BG11 medium. Microalgae cells had high absorption capacity for nitrogen and phosphorus. The nitrogen, phosphorus removal rate of wastewater reached 96.31% and 90.78%, respectively, after 10 days of culture. And the treated wastewater could be used for lactic acid production for four times. These investigations laid a foundation for reducing the pollution of lactic acid wastewater, exploring a late-model for oleaginous microalgae cleaner production.

Integrating micro-algae into wastewater treatment: A review

Improving the ecological status of water sources is a growing focus for many developed and developing nations, in particular with reducing nitrogen and phosphorus in wastewater effluent. In recent years, mixotrophic micro-algae have received increased interest in implementing them as part of wastewater treatment. This is based on their ability to utilise organic and inorganic carbon, as well as inorganic nitrogen (N) and phosphorous (P) in wastewater for their growth, with the desired results of a reduction in the concentration of these substances in the water. The aim of this review is to provide a critical account of micro-algae as an important step in wastewater treatment for enhancing the reduction of N, P and the chemical oxygen demand (COD) in wastewater, whilst utilising a fraction of the energy demand of conventional biological treatment systems. Here, we begin with an overview of the various steps in the treatment process, followed by a review of the cellular and metabolic mechanisms that micro-algae use to reduce N, P and COD of wastewater with identification of when the process may potentially be most effective. We also describe the various abiotic and biotic factors influencing micro-algae wastewater treatment, together with a review of bioreactor configuration and design. Furthermore, a detailed overview is provided of the current state-of-the-art in the use of micro-algae in wastewater treatment.

Role of illumination intensity in microcystin development using Microcystis aeruginosa as the model algae

Microcystis aeruginosa (M. aeruginosa) is one of the most common genera of cyanobacteria in algal blooms. In the present work, the impact of the illumination intensity on the growth of M. aeruginosa has been studied and a grinding method for the extraction of intracellular microcystins (MCs) was developed. The variations of algal density, pH, total phosphorus (TP), and total nitrogen (TN) have been investigated during MCs' culturing period. Results showed that the extraction efficiency of MC-YR by the grinding method was 275% higher than the sonication method, and the extraction efficiencies of MC-RR and MC-LR by the grinding method were similar to the sonication method. The optimal illumination intensity for M. aeruginosa was found to be 19-38 μmol m^-2 s^-1 with suitable pH range of 7.5-10.5. Active release of extracellular MCs was not significantly observed when illumination intensities were ≤ 38 μmol m^-2 s^-1. Furthermore, the intracellular MC yields under different illumination intensities were found to be a relatively stable level. However, excess illumination intensity (≥ 47 μmol m^-2 s^-1) led to the lysis of algal cell and increased the concentrations of extracellular MCs, with MC-RR as the dominant compound. The calculated intracellular/extracellular MCs ratios for MC-RR, MC-LR, and MC-YR were 2.38 (N = 100, SD = 2.44), 2.68 (N = 64, SD = 3.48), and 1.25 (N = 30, SD = 1.64), respectively. Strong illumination intensity and cell lysis were found to be the two major factors influencing the release of extracellular MCs.

Microalgae-based advanced municipal wastewater treatment for reuse in water bodies

Reuse of secondary municipal effluent from wastewater treatment plants in water bodies could effectively alleviate freshwater resource shortage. However, excessive nutrients must be efficiently removed to prevent eutrophication. Compared with other means of advanced wastewater treatment, microalgae-based processes display overwhelming advantages including efficient and simultaneous N and P removal, no requirement of additional chemicals, O₂ generation, CO₂ mitigation, and potential value-added products from harvested biomass. One particular challenge of microalgae-based advanced municipal wastewater treatment compared to treatment of other types of wastewater is that concentrations of nutrients and N:P ratios in secondary municipal effluent are much lower and imbalanced. Therefore, there should be comprehensive considerations on nutrient removal from this specific type of effluent. Removal of nutrients and organic substances, and other environmental benefits of microalgae-based advanced municipal wastewater treatment systems were summarized. Among the existing studies on microalgal advanced nutrient removal, much information on major parameters is absent, rendering performances between studies not really comparable. Mechanisms of microalgae-based nitrogen and phosphorus removal were respectively analyzed to better understand advanced nutrient removal from municipal secondary effluent. Factors influencing microalgae-based nutrient removal were divided into intrinsic, environmental, and operational categories; several factors were identified in each category, and their influences on microalgal nutrient removal were discussed. A multiplicative kinetic model was integrated to estimate microalgal growth-related nutrient removal based majorly on environmental and intrinsic factors. Limitations and prospects of future full-scale microalgae-based advanced municipal wastewater treatment were also suggested. The manuscript could offer much valuable information for future studies on microalgae-based advanced wastewater treatment and water reuse.

Effect of high-temperature stress on microalgae at the end of the logarithmic phase for the efficient production of lipid

Efficient production of microalgae lipid is significant for the production of renewable biodiesel. In the present study, the high temperature of 40°C as stress environment was tested for stimulating lipid accumulation after the microalgae (Scenedesmus quadricauda) cells in suitable conditions grew to the end of the logarithmic phase. Different stress cultivation times of 1, 2, 3, 4, 5 and 6 days were studied. Interestingly, the lipid content and productivity reached 33.5% and 23.2 mg/L d after one day stress cultivation, showing substantial improvements of 39.6% and 33.3% compared with that in the untreated (day 0) microalgae cells, respectively. Longer stress time led to the decrease of biomass and lipid content compared with the untreated microalgae. However, a maximum protein content of 58.7% was obtained after six days. The stress cultivation at the end of the microalgae exponential phase for one day at a high temperature of 40°C could be a very useful industrial approach for efficiently promoting lipid content and biodiesel production.

Feasibility of using brewery wastewater for biodiesel production and nutrient removal by Scenedesmus dimorphus

This work investigates the potential use of a brewery wastewater as a medium for the cultivation of the oleaginous species Scenedesmus dimorphus with the double aim of removing nutrients and to produce biomass as feedstock for biodiesel. For this purpose, effects of nitrogen (61.8-247 mg L(-1)), phosphorous (1.4-5.5 mg L(-1)), and iron (1.5-6 mg L(-1)) concentrations on growth, nutrients uptake, lipid accumulation, and fatty acids profile of this microalga were investigated. Results showed that brewery wastewater can be used as a culture medium even if nitrogen and phosphorous concentrations should have been modified to improve both biomass (6.82 g L(-1)) and lipid accumulation (44.26%). The analysis revealed a C16-C18 composition of 93.47% fatty acids methyl esters with a relative high portion of unsaturated ones (67.24%). High removal efficiency (>99%) for total nitrogen and total phosphorous and a reduction of up to 65% in chemical oxygen demand were achieved, respectively. The final microalgae biomass, considering its high lipid content as well as its compliance with the standards for the quality of biodiesel, and considering also the high removal efficiencies obtained for macronutrients and organic carbon, makes the brewery wastewater a viable option as a priceless medium for the cultivation of microalgae.