Nutrient-driven forward osmosis coupled with microalgae cultivation for energy efficient dewatering of microalgae

Evaluating dye recovery and reusability potential from dyebath effluent using forward osmosis membranes for minimum liquid discharge

This study focuses on the evaluation of dye recovery and reuse potential from denim and polyester effluents using forward osmosis (FO). A cationic surfactant, tetraethylammonium bromide (TEAB), was used as the draw solution (DS). After optimizing the DS and feed solution (FS) concentrations and temperatures in batch experiments, a DS concentration of 0.75 M was selected at a 60 °C temperature for the semi-continuous mode. It generated a high flux of 18 L/m2/h and a low reverse solute flux (RSF) of 0.4 g/m2/h with 100% dye rejection. Dye reconcentration of 82-98% was achieved in the dyebath effluents. The unique property of surfactants to combine hundreds of monomers into micelle resulted in negligible RSF. Reversible fouling was observed on the membrane active layer, and NaOH and citric acid cleaning achieved about 95% of flux recovery. The functional groups on the membrane's active layer remained undisturbed due to foulant interactions showing its chemical stability against reactive dyes. Recovered dye characterization using 1D proton nuclear magnetic resonance (1HNMR) analysis depicted a 100% structural resemblance to the original dye. Hence, it can be reused for dyeing the next batch. Diluted TEAB solution can be used as fabric detergent and softener within the same textile industry in the finishing process. A minimum liquid and persistent pollutant (dyes) discharge is achieved by adopting the methodology proposed in this work with a strong potential of translating it to an industrial scale.

Techno-economic assessment of a novel algal-membrane system versus conventional wastewater treatment and advanced potable reuse processes: Part II

This study developed a comprehensive techno-economic assessment (TEA) framework to evaluate an innovative algae resource recovery and near zero-liquid discharge potable reuse system (i.e., the main system) in comparison with a conventional potable water reuse system (i.e., the benchmark system). The TEA study aims to estimate the levelized costs of water of individual units and integrated processes including secondary wastewater treatment, advanced water purification for potable reuse, and sludge treatment. This would provide decision-makers valuable information regarding the capital and operational costs of the innovative main system versus a typical potable water reuse treatment train, along with possible routes of cost optimization and improvements for the design of full-scale facilities. The main system consists of (i) a novel algal-based wastewater treatment coupled with a dual forward osmosis and seawater reverse osmosis (Algal FO-SWRO) membranes system for potable water reuse and hydrothermal liquefaction (HTL) to produce bioenergy and subsequent nutrients extraction from the harvested algal biomass. The benchmark system includes (ii) an advanced water purification facility (AWPF) that consists of a conventional activated sludge biological treatment (CAS), microfiltration (MF), brackish water reverse osmosis (BWRO), ultraviolet/advanced oxidation process (UV-AOP), and granular activated carbon (GAC), with anaerobic digestion for sludge treatment. Capital expenditures (CAPEX) and operational expenditures (OPEX) were calculated for each unit of both systems (i.e., sub-systems). Based on a 76% overall water recovery designed for the benchmark system, the water cost was estimated at $2.03/m³. The highest costs in the benchmark system were found on the CAS and the anaerobic digester, with the UV-AOP combined with GAC for hydrogen peroxide (H₂O₂) quenching as the driving factor in the increased costs of the system. The cost of the main system, based on an overall 88% water recovery, was estimated to be $1.97/m³, with costs mostly driven by the FO and SWRO membranes. With further cost reduction and optimization for FO membranes such as membrane cost, water recovery, and flux, the main system can provide a much more economically viable alternative in its application than a typical benchmark system.

Life cycle energy use and greenhouse gas emissions for a novel algal-osmosis membrane system versus conventional advanced potable water reuse processes: Part I

This study applied a life cycle assessment (LCA) methodology for a comparative environmental analysis between an innovative algae resource recovery and near zero-liquid discharge potable reuse system (i.e., the main system) versus a conventional potable reuse system (i.e., the benchmark system) through energy use and greenhouse gas (GHG) emissions. The objective of this study is to demonstrate that pilot-scale data coupled with LCA would provide valuable information for system optimization, integration, and improvements for the design of environmentally sustainable full-scale systems. This study also provides decision-makers valuable information regarding the energy demand and environmental impact of this innovative main system compared to a typical tried-and-true system for potable water reuse. The main system consists of a novel algal-based wastewater treatment coupled with a dual forward osmosis and seawater reverse osmosis (Algal FO-SWRO) membranes system for potable water recovery and hydrothermal liquefaction (HTL) to recover biofuels and valuable nutrients from the harvested algal biomass. The benchmark system refers to the current industry standard technologies for potable water reuse and waste management including a secondary biological treatment, microfiltration (MF), brackish water reverse osmosis (BWRO), ultraviolet/advanced oxidation process (UV-AOP), and granular activated carbon (GAC), as well as anaerobic digestion for sludge treatment. Respective energy and GHG emissions of both systems were normalized and compared considering 1 m³ of water recovered. Based on an overall water recovery of 76% designed for the benchmark system, the energy consumption totaled 4.83 kWh/m³, and the system was estimated to generate 2.42 kg of CO₂ equivalent/m³ with most of the emissions coming from the biological treatment. The main system, based on an overall water recovery of 88%, was estimated to consume 4.76 kWh/m³ and emit 1.49 kg of CO₂ eq/m³. The main system has high environmental resilience and can recover bioenergy and nutrients from wastewater with zero waste disposal. With the application of energy recovery devices for the HTL and the SWRO, increase in water recovery of the FO membrane, and replacement of the SWRO membrane with BWRO, the main system provides an energy-competitive and environmentally positive alternative with an energy demand of 2.57 kWh/m³ and low GHG emissions of 0.94 kg CO₂ eq/m³.

Recovering and reuse of textile dyes from dyebath effluent using surfactant driven forward osmosis to achieve zero hazardous chemical discharge

This experimental study explores the feasibility of the reuse of dyes recovered from denim and polyester dyebath effluents using forward osmosis (FO) system to achieve zero hazardous material discharge. In batch experiments, the sodium dodecyl sulfate (SDS) at 0.5 M concentration generated an average flux of 3.5 L/m²/h (LMH) and reverse salt flux (RSF) of only 0.012 g/m²/h (GMH), while maintaining 100% dye rejection. This flux stability comes from the property of surfactants to form micelles and exert a stable osmotic pressure (π) above their critical micelle concentration (CMC). The low RSF is due to the greater micelle size. A colored fouling layer was formed on the membrane active layer (AL), which was easily removed using sodium hydroxide (NaOH) and citric acid. According to Fourier transform infrared spectra and atomic forces microscopy images of the AL, the interaction between foulants and membrane active groups did not significantly affect the physiochemical properties of the membrane. In the semi-continuous experiment, a very stable average flux of 7.3 LMH and RSF of 0.03 GMH was obtained using 0.75 M SDS as draw solution. The stacked 1D proton nuclear magnetic resonance analysis (¹HNMR) spectra of both original and recovered disperse dyes showed 100% similarity, which validates the concept that the recovered dyes maintained their integrity during reconcentration and can be reused in the next batch dyeing process. Importantly, the diluted SDS concentration can be directly reused within the same textile industry in scouring and finishing processes. The processes of dye recovery and reuse developed in this study do not produce any waste or hazardous by-products and are suitable for scale-up and onsite industrial applications.

Microalgae harvesting techniques: updates and recent technological interventions

Microalgal biomass has garnered attention as a renewable and sustainable resource for producing biodiesel. The harvesting of microalgal biomass is a significant bottleneck being faced by the industries as it is the crucial cost driver in the downstream processing of biomass. Bioharvesting of microalgal biomass mediated by: microbial, animal, and plant-based polymeric flocculants has gained a higher probability of utility in accumulation due to: its higher dewatering potential, less toxicity, and ecofriendly properties. The present review summarizes the key challenges and the technological advancements associated with various such harvesting techniques. The economic and technical aspects of different microalgal harvesting techniques, particularly the cationic polymeric flocculant-based harvesting of microalgal biomass, are also discussed. Furthermore, interactions of flocculants with microalgal biomass and the effects of these interactions on metabolite and lipid extractions are discussed to offer a promising solution for suitability in selecting the most efficient and economical method of microalgal biomass harvesting for cost-effective biodiesel production.

Effects of sulfate ions on growth and lipid synthesis of Scenedesmus obliquus in synthetic wastewater with various carbon-to-nitrogen ratios altered by different ammonium and nitrate additions

Producing biodiesel from microalgae is a promising strategy to upgrade energy structure. In this study, effects of sulfate (SO₄^2-) on lipid synthesis of Scenedesmus obliquus (S. obliquus) cultivated in synthetic wastewater with different carbon to nitrogen (C/N) ratios regulated by ammonium (NH₄⁺-N) and nitrate (NO₃^--N), separately, were investigated. The results shown that SO₄^2- could dramatically increase cell growth preferring to NH₄⁺-N supply. And SO₄^2- addition could improve its carbon and nitrogen utilization potential for boosting lipid productivity leading α-linolenic acid (C18:3n3) to occupy a dominant component (38.96%) in NH₄⁺-N group at a C/N ratio of 7.5. Additionally, SO₄^2- could enhance the enrichment and expression of up-regulated genes annotated in key enzymes such as GK, GNPAT, CRLS, plc and DEGS involved in glycerolipid, glycerophospholipid and sphingolipid metabolic pathways, resulting in carbon metabolism enhancement and sulfatide accumulation. This study brings a comprehensive view towards nutritional regulation of lipid synthesis in microalgae.

Membrane-Based Harvesting Processes for Microalgae and Their Valuable-Related Molecules: A Review

The interest in microalgae production deals with its role as the third generation of feedstock to recover renewable energy. Today, there is a need to analyze the ultimate research and advances in recovering the microalgae biomass from the culture medium. Therefore, this review brings the current research developments (over the last three years) in the field of harvesting microalgae using membrane-based technologies (including microfiltration, ultrafiltration and forward osmosis). Initially, the principles of membrane technologies are given to outline the main parameters influencing their operation. The main strategies adopted by the research community for the harvesting of microalgae using membranes are subsequently addressed, paying particular attention to the novel achievements made for improving filtration performance and alleviating fouling. Moreover, this contribution also gives an overview of the advantages of applying membrane technologies for the efficient extraction of the high added-value compounds in microalgae cells, such as lipids, proteins and carbohydrates, which together with the production of renewable biofuels could boost the development of more sustainable and cost-effective microalgae biorefineries.

Enhancement of Biomass Production in Colony-Forming Green Algae, Botryosphaerella sudetica, Under Mixotrophic Cultivation

In this study, we characterized the potential of colony-forming green algae, Botryosphaerella sudetica KNUA107, isolated from Ulleung Island, South Korea, as a bioresource and analyzed the effects of mixotrophic cultivation on its bioresource production efficiency. Internal transcribed spacer (ITS) (ITS1, 5.8S, and ITS2), ribulose bisphosphate carboxylase large subunit (rbcL), and elongation factor Tu (tufa) regions were used for molecular identification and phylogenetic analysis. B. sudetica KNUA107 had a strong relationship with the green algae of Botryococcus and Botryosphaerella genera, which are colony-forming species, and was also associated with members of the Neochloris genus. To improve biomass productivity, we tested mixotrophic cultivation conditions using several organic carbon sources. Glucose supplementation stimulated B. sudetica KNUA107 growth and reduced the time needed to reach the stationary phase. In addition, the colony size was 1.5–2.0 times larger with glucose than in photoautotrophic cultures, and settleability improved in proportion to colony size. The total lipid content and biomass productivity were also higher in cultures supplemented with glucose. Among the lipid components, saturated fatty acids and monounsaturated fatty acids had the highest proportion. Our study suggests that B. sudetica KNUA107, which has enhanced efficiency in biomass production and lipid components under mixotrophic cultivation, has high potential as a bioresource.

Forward Osmosis as Concentration Process: Review of Opportunities and Challenges

In the past few years, osmotic membrane systems, such as forward osmosis (FO), have gained popularity as "soft" concentration processes. FO has unique properties by combining high rejection rate and low fouling propensity and can be operated without significant pressure or temperature gradient, and therefore can be considered as a potential candidate for a broad range of concentration applications where current technologies still suffer from critical limitations. This review extensively compiles and critically assesses recent considerations of FO as a concentration process for applications, including food and beverages, organics value added compounds, water reuse and nutrients recovery, treatment of waste streams and brine management. Specific requirements for the concentration process regarding the evaluation of concentration factor, modules and design and process operation, draw selection and fouling aspects are also described. Encouraging potential is demonstrated to concentrate streams more than 20-fold with high rejection rate of most compounds and preservation of added value products. For applications dealing with highly concentrated or complex streams, FO still features lower propensity to fouling compared to other membranes technologies along with good versatility and robustness. However, further assessments on lab and pilot scales are expected to better define the achievable concentration factor, rejection and effective concentration of valuable compounds and to clearly demonstrate process limitations (such as fouling or clogging) when reaching high concentration rate. Another important consideration is the draw solution selection and its recovery that should be in line with application needs (i.e., food compatible draw for food and beverage applications, high osmotic pressure for brine management, etc.) and be economically competitive.

Mitigating nutrient accumulation with microalgal growth towards enhanced nutrient removal and biomass production in an osmotic photobioreactor

Forward osmosis (FO) has great potential for low energy consumption wastewater reuse provided there is no requirement for draw solutes (DS) regeneration. Reverse solute flux (RSF) can lead to DS build-up in the feed solution. This remains a key challenge because it can cause significant water flux reduction and lead to additional water quality problems. Herein, an osmotic photobioreactor (OsPBR) system was developed to employ fast-growing microalgae to consume the RSF nutrients. Diammonium phosphate (DAP) was used as a fertilizer DS, and algal biomass was a byproduct. The addition of microalgae into the OsPBR proved to maintain water flux while reducing the concentrations of NH₄⁺-N, PO₄^3--P and chemical oxygen demand (COD) in the OsPBR feed solution by 44.4%, 85.6%, and 77.5%, respectively. Due to the forward cation flux and precipitation, intermittent supplements of K⁺, Mg²⁺, Ca²⁺, and SO₄^2- salts further stimulated algal growth and culture densities by 58.7%. With an optimal hydraulic retention time (HRT) of 3.33 d, the OsPBR overcame NH₄⁺-N overloading and stabilized key nutrients NH₄⁺-N at ∼ 2.0 mg L^-1, PO₄^3--P < 0.6 mg L^-1, and COD < 30 mg L^-1. A moderate nitrogen reduction stress resulted in a high carbohydrate content (51.3 ± 0.1%) among microalgal cells. A solids retention time (SRT) of 17.82 d was found to increase high-density microalgae by 3-fold with a high yield of both lipids (9.07 g m^-3 d^-1) and carbohydrates (16.66 g m^-3 d^-1). This study encourages further exploration of the OsPBR technology for simultaneous recovery of high-quality water and production of algal biomass for value-added products.