Evaluation of revolving algae biofilm reactors for nutrients and metals removal from sludge thickening supernatant in a municipal wastewater treatment facility

Efficacy and mechanisms of rotating algal biofilm system in remediation of soy sauce wastewater

This study investigated the efficacy of the rotating algal biofilm (RAB) for treating soy sauce wastewater (SW) and its related treatment mechanisms. The RAB system demonstrated superior nutrient removal (chemical oxygen demand, ammonium nitrogen, total nitrogen, and phosphorus for 92 %, 94 %, 91 %, and 82 %, respectively) and biofilm productivity (14 g m-2 d-1) at optimized 5-day harvest time and 2-day hydraulic retention time. This was mainly attributed to the synergistic interactions within the algae-fungi (Apiotrichum)-bacteria (Acinetobacter and Rhizobia) consortium, which effectively assimilated certain extracellular polymeric substances into biomass to enhance algal biofilm growth. Increased algal productivity notably improved protein and essential amino acid contents in the biomass, suggesting a potential for animal feed applications. This study not only demonstrates a sustainable approach for managing SW but also provides insight into the nutrient removal and biomass conversion, offering a viable strategy for large-scale applications in nutrient recovery and wastewater treatment.

Design, construction and application of algae-bacteria synergistic system for treating wastewater

The wastewater treatment technology of algae-bacteria synergistic system (ABSS) is a promising technology which has the advantages of low energy consumption, good treatment effect and recyclable high-value products. In this treatment technology, the construction of an ABSS is a very important factor. At the same time, the emergence of some new technologies (such as microbial fuel cells and bio-carriers, etc.) has further enriched constructing the novel ABSS, which could improve the efficiency of wastewater treatment and the biomass harvesting rate. Thus, this review focuses on the construction of a novel ABSS in wastewater treatment in order to provide useful suggestions for the technology of wastewater treatment.

Enhancement of Mn2+, Fe2+ and NH4+-N removal by biochar synergistic strains combined with activated sludge in real wastewater treatment

Acinetobacter sp. AL-6 combining with biochar was adapted in activated sludge (AS & co-system) to decontaminate Mn2+, Fe2+ and NH4+-N, and treat activated sludge (AS) for its activity and settling performance improvement. Specifically, the co-system promoted the growth of bacteria in the activated sludge, thus increasing its ability to nitrify and adsorb Mn2+ and Fe2+, resulting in the removal of high concentrations of NH4+-N, Mn2+, Fe2+ and COD in the reactor by 100%, 100%, 100%, and 96.8%, respectively. And the pH of wastewater was increased from 4 to 8.5 by co-system also facilitated the precipitation of Mn2+ and Fe2+. The MLVSS/MLSS ratio increased from 0.64 to 0.95 and SVI30 decreased from 92.54 to 1.54 after the addition of co-system, which indicated that biochar helped to improve the activity and settling performance of activated sludge and prevented it from being damaged by the compound Mn2+ and Fe2+. In addition, biochar promoted the increase of the tyrosine-like protein substance and humic acid-like organic matter in the sludge EPS, thus enhanced the ability of sludge to adsorb Mn2+ and Fe2+. Concretely, compared with AS group, the proteins content and polysaccharides content of the AS & co-system group were increased by 13.14 times and 6.30 times respectively. Further, microbial diversity analysis showed that more resistant bacteria and dominant bacteria Acinetobacter sp. AL-6 in sludge enhanced the nitrification and adsorption of manganese and iron under the promotion of biochar. Pre-eminently, the more effective AS & co-system were applied to the removal of actual electrolytic manganese slag leachate taken from the contaminated site, and the removal of NH4+-N, Mn2+, Fe2+ and COD remained high at 100%, 100%, 71.82% and 94.72%, respectively, revealing advanced value for high engineering applications of AS & co-system.

Biofilm and suspension-based cultivation of microalgae to treat anaerobic digestate food effluent (ADFE)

Anaerobic digestion of organic waste produces effluent (ADE) that requires further treatment. Biofilm-based microalgal cultivation is a favoured approach to ADE treatment. This study compared Chlorella sp. MUR 268 and Scenedesmus sp. MUR 269 in biofilm and suspension cultures to treat anaerobic digestate food effluent (ADFE). Chlorella sp. MUR 268 biofilm had significantly higher biomass (50.38 g m-2) than Scenedesmus sp. biofilm (9.39 g m-2). Conversely, Scenedesmus sp. yielded 1.5 times more biomass (1.2 g L-1) than Chlorella sp. in suspension. Chlorella sp. biofilm had 49.3 % higher areal productivity than suspension, while Scenedesmus sp. showed 87.3 % higher areal growth in suspension. Chlorella sp. MUR 268 and Scenedesmus sp. MUR 269 significantly removed nutrients in ADFE. In suspension, COD, ammoniacal nitrogen, and phosphate were reduced to 94.9, 5.2, and 5.98 mg L-1 for Chlorella sp. MUR 268, and 245, 2.89, and 3.22 mg L-1 for Scenedesmus sp. MUR 269, respectively. In biofilm, Chlorella sp. MUR 268 achieved reductions to 149.9, 1.16, and 3.57 mg L-1, while Scenedesmus sp. MUR 269 achieved 100.2, 6.9 and 2.07 mg L-1. Most of these values are below the recommended effluent discharge standard, highlighting the efficacy of this system in ADFE treatment. Biofilm cultures fixed 68-81 % of removed nitrogen in biomass, while in suspension, only 55-71 % ended in the biomass. Chlorella sp. MUR 268 biofilm fixed 88 % of removed phosphorus, while Scenedesmus sp. MUR 269 suspension fixed more phosphorus (55 %) than the biofilm counterpart (34 %). This biofilm design offers advantages like simplified, cost-effective operation, easy biomass recovery, and reduced water usage.

Synergistic interactions of light and dark biofilms in rotating algal biofilm system for enhanced aquaculture wastewater treatment

Aquaculture wastewater management is critical for environmental sustainability. This study investigates the synergistic interactions between light and dark biofilms with a Rotating Algal Biofilm (RAB) system for effective aquaculture wastewater treatment. The RAB system, optimized with a 5-day harvest time and 12-hour hydraulic retention time, demonstrated superior biomass productivity (3.3 g m-2 d-1) and total ammoniacal nitrogen removal (82.3 %). Comparative analysis of light and dark biofilms revealed their complementary roles, with the light side exhibiting higher carbon assimilation and nutrient removal efficiencies, while the dark side contributed significantly to denitrification and phosphorus removal. Microbial community analysis highlighted the dominance of key bacterial genera such as Haliangium, Methyloversatilis and Comamonadaceae, along with the algal genus Chlorella, indicating their crucial roles in nutrient cycling. This study provides insights into the operational dynamics of RAB system for sustainable aquaculture wastewater treatment.

Scale-up of microalgal systems for decarbonization and bioproducts: Challenges and opportunities

The threat of global climate change presents a significant challenge for humanity. Microalgae-based carbon capture and utilization (CCU) technology has emerged as a promising solution to this global issue. This review aims to comprehensively evaluate the current advancements in scale-up of microalgae cultivation and its applications, specifically focusing on decarbonization from flue gases, organic wastewater remediation, and biogas upgrading. The study identifies critical challenges that need to be addressed during the scale-up process and evaluates the economic viability of microalgal CCU within the carbon market. Additionally, it analyzes the commercial status of microalgae-derived products and highlights those with high market demand. This review serves as a crucial resource for researchers, industry professionals, and policymakers to develop and implement innovative approaches to enhance the efficiency of microalgae-based CO2 utilization while addressing the challenges associated with the scale-up of microalgae technologies.

Cultivation of microalgae in food processing effluent for pollution attenuation and astaxanthin production: a review of technological innovation and downstream application

Valorization of food processing effluent (FPE) by microalgae cultivation for astaxanthin production is regarded as a potential strategy to solve the environmental pollution of food processing industry and promote the development of eco-friendly agriculture. In this review paper, microalgal species which have the potential to be employed for astaxanthin in FPE were identified. Additionally, in terms of CO2 emission, the performances of microalgae cultivation and traditional methods for FPE remediation were compared. Thirdly, an in-depth discussion of some innovative technologies, which may be employed to lower the total cost, improve the nutrient profile of FPE, and enhance the astaxanthin synthesis, was provided. Finally, specific effects of dietary supplementation of algal astaxanthin on the growth rate, immune response, and pigmentation of animals were discussed. Based on the discussion of this work, the cultivation of microalgae in FPE for astaxanthin production is a value-adding process which can bring environmental benefits and ecological benefits to the food processing industry and agriculture. Particularly, technological innovations in recent years are promoting the shift of this new idea from academic research to practical application. In the coming future, with the reduction of the total cost of algal astaxanthin, policy support from the governments, and further improvement of the innovative technologies, the concept of growing microalgae in FPE for astaxanthin will be more applicable in the industry.

Efficient nitrogen removal from real municipal wastewater and mature landfill leachate using partial nitrification-simultaneous anammox and partial denitrification process

Anaerobic ammonia oxidation (anammox) of municipal wastewater is a research focus, especially the combined treatment with mature landfill leachate is a current research hotspot. In this study, municipal wastewater was treated by partial nitrification via sequencing batch reactor (SBR), and its effluent and mature landfill leachate were then mixed into an up-flow anaerobic sludge blanket (UASB) for simultaneous anammox and partial denitrification reaction. Through partial nitrification, a high nitrite accumulation rate (93.0 ± 3.8 %) was achieved by low dissolved oxygen (0.5-1.6 mg/L) and controlled aerobic time (3.5 h) in SBR. The UASB system was responsible for 78.8 ± 2.1 % nitrogen removal of the entire system with a hydraulic reaction time (HRT) of 3.8 h, accompanied by the anammox contribution up to 89.4 ± 6.0 %. The overall partial nitrification-simultaneous anammox and partial denitrification (PN-SAPD) system was controlled at a total COD/TIN of 2.8 ± 0.3 and a total HRT of only 10.2 h, achieving the nitrogen removal efficiency and effluent TIN were 95.2 ± 2.2 % and 3.4 ± 1.5 mg/L, respectively. The qPCR results showed functional genes (hzsA(B), hdh) associated with anaerobic ammonia-oxidizing bacteria (AnAOB), whose high gene copy abundance and transcription expression ensured the removal of major nitrogen from municipal wastewater and mature landfill leachate. 16S amplicon sequencing showed that the Ca. Brocadia (9.72-12.6 %) was further enrichment after sodium acetate was added, and the transcription expression of Thauera (0.5-7.0 %) caused nitrate to nitrite. The high abundance of related enzymes (hao, hzs, hdh, narGHI) involved in anammox and partial denitrification processes were found in the macrogenomic sequencing, and only Ca. Brocadia was involved in multi-pathway nitrogen metabolism in AnAOB. Based on the efficient nitrogen removal by AnAOB and denitrifying bacteria, this modified PN-SAPD process provides a new option for the co-treatment of mature landfill leachate in municipal wastewater treatment plants.

Emerging revolving algae biofilm system for algal biomass production and nutrient recovery from wastewater

Toward the direction of zero‑carbon emission and green technologies for wastewater treatment, algae-based technologies are considered promising candidates to deal with the current situation of pollution and climate change. Recent developments of algae-based technologies have been introduced in previous studies in which their performances were optimized for wastewater treatment and biomass production. Among these, revolving algae biofilm (RAB) reactors have been proven to have a great potential in high biomass productivity, simple harvesting method, great CO2 transfer rate, high light-use efficiency, heavy metal capture, nutrient removal, and acid mine drainage treatment in previous studies. However, there were few articles detailing RAB performance, which concealed its enormous potential and diminished interest in the model. Hence, this review aims to reveal the major benefit of RAB reactors in simultaneous wastewater treatment and biomass cultivation. However, there is still a lack of research on aspects to upgrade this technology which requires further investigations to improve performance or fulfill the concept of circular economy.

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.

Treatment of mixed wastewater by vertical rotating microalgae-bacteria symbiotic biofilm reactor

A novel vertical rotating microalgae-bacteria symbiotic biofilm reactor was built to treat the mixed wastewater containing municipal and soybean soaking wastewater. The reactor was operated in both sequential batch and semi-continuous modes. Under the sequential batch operation mode, the maximum removal rates for Chemical Oxygen Demand (COD), Total Nitrogen (TN), Total Phosphorus (TP), and Ammonia Nitrogen (NH4+-N) of the mixed wastewater were 95.6 %, 96.1 %, 97.6 %, and 100 %, respectively. During the semi-continuous operation, the water discharge indices decreased gradually and eventually stabilized. At stabilization, the removal rates of COD, TN, and NH4+-N achieved 98 %, 95 %, and 99.9 %, respectively. The maximum biomass productivity of the biofilm was 2.69 g·m-2·d-1. Additionally, the carbohydrate, protein and lipid comprised approximately 22 %, 51 % and 10 % of the dry weight of Chlorella. This study demonstrates the great potential of the microalgae-bacteria symbiotic biofilm system to treat food and domestic wastewater while harvesting microalgal biomass.

Microalgal-bacterial biofilms for wastewater treatment: Operations, performances, mechanisms, and uncertainties

Microalgal-bacterial biofilms have been increasingly considered of great potential in wastewater treatment due to the advantages of microalgal-bacterial synergistic pollutants removal/recovery, CO2 sequestration, and cost-effective biomass-water separation. However, such advantages may vary widely among different types of microalgal-bacterial biofilms, as the biofilms could be formed on different shapes and structures of attachment substratum, generating "false hope" for certain systems in large-scale wastewater treatment if the operating conditions and pollutants removal properties are evaluated based on the general term "microalgal-bacterial biofilm". This study, therefore, classified microalgal-bacterial biofilms into biofilms formed on 2D substratum, biofilms formed on 3D substratum, and biofilms formed without substratum (i.e. microalgal-bacterial granular sludge, MBGS). Biofilms formed on 2D substratum display higher microalgae fractions and nutrients removal efficiencies, while the adopted long hydraulic retention times were unacceptable for large-scale wastewater treatment. MBGS are featured with much lower microalgae fractions, most efficient pollutants removal, and acceptable retention times for realistic application, yet the feasibility of using natural sunlight should be further explored. 3D substratum systems display wide variations in operating conditions and pollutants removal properties because of diversified substratum shapes and structures. 2D and 3D substratum biofilms share more common in eukaryotic and prokaryotic microbial community structures, while MGBS biofilms are more enriched with microorganisms favoring EPS production, biofilm formation, and denitrification. The specific roles of stratified extracellular polymeric substances (EPS) in nutrients adsorption and condensation still require in-depth exploration. Nutrients removal uncertainties caused by microalgal-bacterial synergy decoupling under insufficient illumination, limited microbial community control, and possible greenhouse gas emission exacerbation arising from microalgal N2O generation were also indicated. This review is helpful for revealing the true potential of applying various microalgal-bacterial biofilms in large-scale wastewater treatment, and will provoke some insights on the challenges to the ideal state of synergistic pollutants reclamation and carbon neutrality via microalgal-bacterial interactions.

A critical review on phycoremediation of pollutants from wastewater-a novel algae-based secondary treatment with the opportunities of production of value-added products

Though the biological treatment employing bacterial strains has wide application in effluent treatment plant, it has got several limitations. Researches hence while looking for alternative biological organisms that can be used for secondary treatment came up with the idea of using microalgae. Since then, a large number of microalgal/cyanobacterial strains have been identified that can efficiently remove pollutants from wastewater. Some researchers also found out that the algal biomass not only acts as a carbon sink by taking up carbon dioxide from the atmosphere and giving oxygen but also is a renewable source of several value-added products that can be extracted from it for the commercial use. In this work, the cleaning effect of different species of microalgae/cyanobacteria on wastewater from varied sources along with the value-added products obtained from the algal biomass as observed by researchers during the past few years are reviewed. While a number of review works in the field of phycoremediation technology was reported in literature, a comprehensive study on phycoremediation of wastewater from different industries and household individually is limited. In the present review work, the efficiency of diverse microalgal/cyanobacterial strains in treatment of wide range of industrial effluents along with municipal wastewater having multi-pollutants has been critically reviewed.

Growth of Scenedesmus obliquus on anaerobic soybean wastewater using different wasted organics for high biomass production and nutrients recycling

The microalgae culture in mixing sewage with different characteristics may significantly improve biomass production and nutrients recycling efficiency. In this study, three waste organic wastewater including molasses, alcohol and glycerol wastewater were mixed with anaerobic soybean wastewater as mediums for microalgae culture. The optimal mixture of molasses, alcohol and glycerol wastewater was at an initial carbon-nitrogen ratio of 7:1, 5:1 and 10:1, improving biomass production by 60.4%, 31.3% and 68.7%, respectively. The removal efficiencies of organics, ammonia nitrogen and phosphorus at optimal mixture were 54.8-62.4%, 79.5-99.1% and 49.3-61.5%, and the removal rates increased by 340-630%, 27.5-66.3% and 36.3-70.2% compared to the blank culture. In addition, the culture in mixed wastewater increased lipids contrast by 0.7-1.3 times, while achieving higher saturation in fatty acids. The results suggested that microalgae culture using mixed wastewater was a strategy for high biomass production and nutrients recycling efficiency.

Isolation of phosphorus-hyperaccumulating microalgae from revolving algal biofilm (RAB) wastewater treatment systems

Excess phosphorus (P) in wastewater effluent poses a serious threat to aquatic ecosystems and can spur harmful algal blooms. Revolving algal biofilm (RAB) systems are an emerging technology to recover P from wastewater before discharge into aquatic ecosystems. In RAB systems, a community of microalgae take up and store wastewater P as polyphosphate as they grow in a partially submerged revolving biofilm, which may then be harvested and dried for use as fertilizer in lieu of mined phosphate rock. In this work, we isolated and characterized a total of 101 microalgae strains from active RAB systems across the US Midwest, including 82 green algae, 9 diatoms, and 10 cyanobacteria. Strains were identified by microscopy and 16S/18S ribosomal DNA sequencing, cryopreserved, and screened for elevated P content (as polyphosphate). Seven isolated strains possessed at least 50% more polyphosphate by cell dry weight than a microalgae consortium from a RAB system, with the top strain accumulating nearly threefold more polyphosphate. These top P-hyperaccumulating strains include the green alga Chlamydomonas pulvinata TCF-48 g and the diatoms Eolimna minima TCF-3d and Craticula molestiformis TCF-8d, possessing 11.4, 12.7, and 14.0% polyphosphate by cell dry weight, respectively. As a preliminary test of strain application for recovering P, Chlamydomonas pulvinata TCF-48 g was reinoculated into a bench-scale RAB system containing Bold basal medium. The strain successfully recolonized the system and recovered twofold more P from the medium than a microalgae consortium from a RAB system treating municipal wastewater. These isolated P-hyperaccumulating microalgae may have broad applications in resource recovery from various waste streams, including improving P removal from wastewater.

Trends in microalgal-based systems as a promising concept for emerging contaminants and mineral salt recovery from municipal wastewater

In the context of climate change leading to water scarcity for many people in the world, the treatment of municipal wastewater becomes a necessity. However, the reuse of this water requires secondary and tertiary treatment processes to reduce or eliminate a load of dissolved organic matter and various emerging contaminants. Microalgae have shown hitherto high potential applications of wastewater bioremediation thanks to their ecological plasticity and ability to remediate several pollutants and exhaust gases from industrial processes. However, this requires appropriate cultivation systems allowing their integration into wastewater treatment plants at appropriate insertion costs. This review aims to present different open and closed systems currently used in the treatment of municipal wastewater by microalgae. It provides an exhaustive approach to wastewater treatment systems using microalgae, integrating the most suitable used microalgae species and the main pollutants present in the treatment plants, with an emphasis on emerging contaminants. The remediation mechanisms as well as the capacity to sequester exhaust gases were also described. The review examines constraints and future perspectives of microalgae cultivation systems in this line of research.

Sidestream characteristics in water resource recovery facilities: A critical review

This review compiles information on sidestream characteristics that result from anaerobic digestion dewatering (conventional and preceded by a thermal hydrolysis process), biological and primary sludge thickening. The objective is to define a range of concentrations for the different characteristics found in literature and to confront them with the optimal operating conditions of sidestream processes for nutrient treatment or recovery. Each characteristic of sidestream (TSS, VSS, COD, N, P, Al³⁺, Ca²⁺, Cl^-, Fe^2+/3+, Mg²⁺, K⁺, Na⁺, SO₄^2-, heavy metals, micro-pollutants and pathogens) is discussed according to the water resource recovery facility configuration, wastewater characteristics and implications for the recovery of nitrogen and phosphorus based on current published knowledge on the processes implemented at full-scale. The thorough analysis of sidestream characteristics shows that anaerobic digestion sidestreams have the highest ammonium content compared to biological and primary sludge sidestreams. Phosphate content in anaerobic digestion sidestreams depends on the type of applied phosphorus treatment but is also highly dependent on precipitation reactions within the digester. Thermal Hydrolysis Process (THP) mainly impacts COD, N and alkalinity content in anaerobic digestion sidestreams. Surprisingly, the concentration of phosphate is not higher compared to conventional anaerobic digestion, thus offering more attractive recovery possibilities upstream of the digester rather than in sidestreams. All sidestream processes investigated in the present study (struvite, partial nitrification/anammox, ammonia stripping, membranes, bioelectrochemical system, electrodialysis, ion exchange system and algae production) suffer from residual TSS in sidestreams. Above a certain threshold, residual COD and ions can also deteriorate the performance of the process or the purity of the final nutrient-based product. This article also provides a list of characteristics to measure to help in the choice of a specific process.

Study of Solidifying Surplus Sludge as Building Material Using Ordinary Portland Cement

In an attempt to effectively utilize a multitude of surplus sludge from sewage treatment plants, ordinary Portland cement was used to solidify the dry surplus sludge as a building material. The dry surplus sludge and cement were mixed at different proportions with a certain dosage of water and then cured for 3–60 days at room temperature. The unconfined compression strength (RC) of solidified blocks was investigated with respect to the effects of the ratio of liquid to solid (Rl/S), surplus sludge dosage (DS), the dosage of sodium silicate (DNa2SiO3), and the proportion of fly ash (WF). The fabricated solidified blocks were characterized by scanning electron microscopy (SEM), Fourier transform-infrared spectroscopy (FT-IR), and X-ray Diffraction Analysis (XRD). The results demonstrated that RC at 60 days reduced obviously with the increase in Rl/s when Ds was given, whereas RC reduced with DS increased to 15.0 wt% from 5.0 wt% for solidified blocks. When DS was 5.0 wt%, RC of 28 days was reduced from 20.87 MPa to 14.50 MPa, with an increase in Rl/s from 0.35 to 0.55. For the given Rl/s, such as Rl/s = 0.35, RC at 60 days was 23.75 MPa, 2.80 MPa, and 2.50 MPa when DS were 5.0 wt%, 10.0 wt%, and 15.0 wt%, respectively, which were relatively lower in comparison to that of Portland cement solidified blocks without surplus sludge (51.40 MPa). In addition, the addition of Na2SiO3 and fly ash was favorable in terms of improving the RC for solidified blocks. RC of 60 days increased initially and then reduced with the increase in DNa2SiO3 from 0.0 wt% to 9.0 wt% at Rl/s = 0.45 and DS = 5.0 wt%. At DNa2SiO3 = 7.5 wt%, Rl/s = 0.45, and DS = 5.0 wt%, the highest RC value of 34.70 MPa was achieved after being cured for 60 days. Furthermore, RC of 60 days increased initially and then reduced with WF increasing from 0.0 wt% to 25.0 wt%, and the highest RC value of 34.35 MPa was achieved at WF = 10.0 wt%, Rl/s = 0.45, and DS = 5.0 wt%. At the ratio of DNa2SiO3 = 7.50 wt%, Rl/S = 0.35, WF = 20 wt%, DS = 15.0 wt% and M = 1.00, RC of 28 days reached 26.70 MPa. With these values, the utilization of sludge utilized (DS = 15.0 wt%) was increased by double compared with DS = 5.0 wt% (20.87 MPa). To investigate the effect of environmental temperature on the mechanical properties and mass of solidified blocks, the freeze-thaw cycling experiment was carried out. The RC of 28 days and the mass of the solidified block reduced with the number of freeze-thaw cycles, increasing for solidified blocks with DS of 5.0 wt%, 10.0 wt%, and 15.0 wt%, manifesting a decrease of 25.60%, 32.30%, and 40.60% for RC and 3.40%, 4.10%, and 4.90% for mass, respectively. This work provides sufficient evidence that surplus sludge has a huge potential application for building materials from the perspective of improving their mechanical properties. It provides an important theoretical basis for the disposal as well as efficient utilization of sludge.

A revolving algae biofilm based photosynthetic microbial fuel cell for simultaneous energy recovery, pollutants removal, and algae production

Photosynthetic microbial fuel cell (PMFC) based on algal cathode can integrate of wastewater treatment with microalgal biomass production. However, both the traditional suspended algae and the immobilized algae cathode systems have the problems of high cost caused by Pt catalyst and ion-exchange membrane. In this work, a new equipment for membrane-free PMFC is reported based on the optimization of the most expensive MFC components: the separator and the cathode. Using a revolving algae-bacteria biofilm cathode in a photosynthetic membrane-free microbial fuel cell (RAB-MFC) can obtain pollutants removal and algal biomass production as well as electrons generation. The highest chemical oxygen demand (COD) removal rates of the anode and cathode chambers reached 93.5 ± 2.6% and 95.8% ± 0.8%, respectively. The ammonia removal efficiency in anode and cathode chambers was 91.1 ± 1.3% and 98.0 ± 0.6%, respectively, corresponding to an ammonia removal rate of 0.92 ± 0.02 mg/L/h. The maximum current density and power density were 136.1 mA/m2 and 33.1 mW/m2. The average biomass production of algae biofilm was higher than 30 g/m2. The 18S rDNA sequencing analysis the eukaryotic community and revealed high operational taxonomic units (OTUs) of Chlorophyta (44.43%) was dominant phyla with low COD level, while Ciliophora (54.36%) replaced Chlorophyta as the dominant phyla when COD increased. 16S rDNA high-throughput sequencing revealed that biofilms on the cathode contained a variety of prokaryote taxa, including Proteobacteria, Bacteroidota, Firmicutes, while there was only 0.23-0.26% photosynthesizing prokaryote found in the cathode biofilm. Collectively, this work demonstrated that RAB can be used as a bio-cathode in PMFC for pollutants removal from wastewater as well as electricity generation.

A Review on the Reliability and the Readiness Level of Microalgae-Based Nutrient Recovery Technologies for Secondary Treated Effluent in Municipal Wastewater Treatment Plants

Algae-based wastewater treatment technologies are promising green technologies with huge economical potential and environmental co-benefits. However, despite the immense research, work, and achievement, no publications were found wherein these technologies have been successfully applied in an operational environment for nitrogen and phosphorus removal of secondary treated effluent in municipal wastewater treatment plants. Based on a literature review and targeted comprehensive analysis, the paper seeks to identify the main reasons for this. The reliability (considering inlet wastewater quality variations, operating conditions and process control, algae harvesting method, and produced biomass) as well as the technology readiness level for five types of reactors are discussed. The review shows that the reactors with a higher level of control over the technological parameters are more reliable but algal post-treatment harvesting and additional costs are barriers for their deployment. The least reliable systems continue to be attractive for research due to the non-complex operation and relieved expenditure costs. The rotating biofilm systems are currently undertaking serious development due to their promising features. Among the remaining research gaps and challenges for all the reactor types are the identification of the optimal algal strains, establishment of technological parameters, overcoming seasonal variations in the effluent’s quality, and biomass harvesting.

Community-level and function response of photoautotrophic periphyton exposed to oxytetracycline hydrochloride

Periphyton is considered important for removal of organic pollutants from water bodies, but knowledge of the impacts of antibiotics on the community structure and ecological function of waterbodies remains limited. In this study, the effects of oxytetracycline hydrochloride (OTC) on the communities of photoautotrophic epilithon and epipelon and its effect on nitrogen and phosphorus concentrations in the water column were studied in a 12-day mesocosm experiment. The dynamics of nitrogen and phosphorus concentrations in the epipelon and epilithon experiment showed similar patterns. The concentrations of total nitrogen, dissolved total nitrogen, ammonium nitrogen, total phosphorus and dissolved total phosphorus in the water column increased rapidly during the initial days of exposure, after which a downward trend occurred. In the epilithon experiment, we found that the photosynthesis (Fv/Fm) and biomass of epilithon were significantly (P < 0.05) stimulated in the low concentration group. Contrarily, growth and photosynthesis (Fv/Fm) were significantly (P < 0.05) reduced in the medium and high concentration group. We further found that the photosynthetic efficiency of photoautotrophic epilithon was negatively correlated with the concentrations of nitrogen and phosphorus in the water column (P < 0.05). Principal coordinate analysis (PCoA) showed that the communities of epilithic algae in the control group and in the low concentration group were significantly (P < 0.05) different from that of the high concentration group during the initial 4 days. After 8 days' exposure, all groups tended to be similar, indicating that epilithon showed rapid adaptability and/or resilience. Similar results were found for the relative abundance of some epilithic algae. Our findings indicate that the biofilm system has strong tolerance and adaptability to OTC as it recovered fast after an initial suppression, thus showing the important role of periphyton in maintaining the dynamic balance of nutrients with other processes in aquatic ecosystems.

Pharmaceuticals and personal care products in aquatic environments and their removal by algae-based systems

The consumption of pharmaceuticals and personal care products (PPCPs) has been widely increasing, yet up to 90-95% of PPCPs consumed by human are excreted unmetabolized. Moreover, the most of PPCPs cannot be fully removed by wastewater treatment plants (WWTPs), which release PPCPs to natural water bodies, affecting aquatic ecosystems and potentially humans. This study sought to review the occurrence of PPCPs in natural water bodies globally, and assess the effects of important factors on the fluxes of pollutants into receiving waterways. The highest ibuprofen concentration (3738 ng/L) in tap water was reported in Nigeria, and the highest naproxen concentration (37,700 ng/L) was reported in groundwater wells in Penn State, USA. Moreover, the PPCPs have affected aquatic organisms such as fish. For instance, up to 24.4 × 10³ ng/g of atenolol was detected in P. lineatus. Amongst different technologies to eliminate PPCPs, algae-based systems are environmentally friendly and effective because of the photosynthetic ability of algae to absorb CO₂ and their flexibility to grow in different wastewater. Up to 99% of triclosan and less than 10% of trimethoprim were removed by Nannochloris sp., green algae. Moreover, variable concentrations of PPCPs might adversely affect the growth and production of algae. The exposure of algae to high concentrations of PPCPs can reduce the content of chlorophyll and protein due to producing reactive oxygen species (ROS), and affecting expression of some genes in chlorophyll (rbcL, psbA, psaB and psbc).

Shining a Light on Wastewater Treatment with Microalgae

Microalgae can produce biofuels, nutriceuticals, pigments and many other products, but commercialization has been limited by the cost of growing, harvesting and processing algal biomass. Nutrients, chiefly nitrogen and phosphorus, are a key cost for growing microalgae, but these nutrients are present in abundance in municipal wastewater where they pose environmental problems if not removed. This is not a traditional review article; rather, it is a fact-based set of suggestions that will have to be investigated by scientists and engineers. It is suggested that if microalgae were grown as biofilms rather than as planktonic cells, and if internal illumination rather than external illumination were employed, then the use of microalgae may provide useful improvements to the wastewater treatment process. The use of microalgae to remove nutrients from wastewater has been demonstrated, but has not yet been widely implemented due to cost, and because microalgae derived from wastewater treatment has not yet been demonstrated as a commercial source for value-added products. Future facilities are likely to be called Municipal Resource Recovery Facilities as wastewater will increasingly be viewed as a resource for water, biofuels, fertilizer, monitoring public health and value-added products. Advances in photonics will accelerate this transition.

Pollution prevention and waste phycoremediation by algal-based wastewater treatment technologies: The applications of high-rate algal ponds (HRAPs) and algal turf scrubber (ATS)

Following the escalating human population growth and rapid urbanization, the tremendous amount of urban and industrial waste released leads to a series of critical issues such as health issues, climate change, water crisis, and pollution problems. With the advantages of a favorable carbon life cycle, high photosynthetic efficiencies, and being adaptive to harsh environments, algae have attracted attention as an excellent agent for pollution prevention and waste phycoremediation. Following the concept of circular economy and biorefinery for sustainable production and waste minimization, this review discusses the role of four different algal-based wastewater treatment technologies, including high-rate algal ponds (HRAPs), HRAP-absorption column (HRAP-AC), hybrid algal biofilm-enhanced raceway pond (HABERP) and algal turf scrubber (ATS) in waste management and resource recovery. In addition to the nutrient removal mechanisms and operation parameters, recent advances and developments have been discussed for each technology, including (1) Innovative operation strategies and treatment of emerging contaminants (ECs) employing HRAPs, (2) Biogas upgrading utilizing HRAP-AC system and approaches of O₂ minimization in biomethane, (3) Operation of different HABERP systems, (4) Life-cycle and cost analysis of HRAPs-based wastewater treatment system, and (5) Value-upgrading for harvested algal biomass and life-cycle cost analysis of ATS system.

Potential of Microalgae in Bioremediation of Wastewater

The increase in global pollution, industrialization and fast economic progress are considered to inflict serious consequences to the quality and availability of water throughout the world. Wastewater is generated from three major sources, i.e. industrial, agricultural, and municipal which contain pollutants, such as: xenobiotics, microplastics, heavy metals and augmented by high amount of carbon, phosphorus, and nitrogen compounds. Wastewater treatment is one of the most pressing issues since it cannot be achieved by any specific technology because of the varying nature and concentrations of pollutants and efficiency of the treatment technologies. The degradation capacity of these conventional treatment technologies is limited, especially regarding heavy metals, nutrients, and xenobiotics, steering the researchers to bioremediation using microalgae (Phycoremediation). Bioremediation can be defined as use of microalgae  for removal or biotransformation of pollutants and CO2 from wastewater with concomitant biomass production. However, the usage of wastewaters for the bulk cultivation of microalgae is advantageous for reducing carbon, nutrients cost, minimizing the consumption of freshwater, nitrogen, phosphorus recovery, and removal of other pollutants from wastewater and producing sufficient biomass for value addition for either biofuels or other value-added compounds. Several types of microalgae like Chlorella and Dunaliella have proved their applicability in the treatment of wastewaters. The bottlenecks concerning the microalgal wastewater bioremediation need to be identified and elucidated to proceed in bioremediation using microalgae. This objective of this paper is to provide an insight about the treatment of different wastewaters using microalgae and microalgal potential in the treatment of wastewaters containing heavy metals and emerging contaminants, with the specialized cultivation systems. This review also summarizes the end use applications of microalgal biomass which makes the bioremediation aspect more environmentally sustainable. Copyright © 2021 by Authors, Published by BCREC Group. This is an open access article under the CC BY-SA License (https://creativecommons.org/licenses/by-sa/4.0). 

Phosphate Elimination and Recovery Lightweight (PEARL) membrane: A sustainable environmental remediation approach

Aqueous phosphate pollution can dramatically impact ecosystems, introducing a variety of environmental, economic, and public health problems. While novel remediation tactics based on nanoparticle binding have shown considerable promise in nutrient recovery from water, they are challenging to deploy at scale. To bridge the gap between the laboratory-scale nature of these nanostructure solutions and the practical benchmarks for deploying an environmental remediation tool, we have developed a nanocomposite material. Here, an economical, readily available, porous substrate is dip coated using scalable, water-based processes with a slurry of nanostructures. These nanomaterials have tailored affinity for specific adsorption of pollutants. Our Phosphate Elimination and Recovery Lightweight (PEARL) membrane can selectively sequester up to 99% of phosphate ions from polluted waters at environmentally relevant concentrations. Moreover, mild tuning of pH promotes at will adsorption and desorption of nutrients. This timed release allows for phosphate recovery and reuse of the PEARL membrane repeatedly for numerous cycles. We combine correlative microscopy and spectroscopy techniques to characterize the complex microstructure of the PEARL membrane and to unravel the mechanism of phosphate sorption. More broadly, through the example of phosphate pollution, this work describes a platform membrane approach based on nanostructures with specific affinity coated on a porous structure. Such a strategy can be tuned to address other environmental remediation challenges through the incorporation of other nanomaterials.

Algae Biofilm Reduces Microbe-Derived Dissolved Organic Nitrogen Discharges: Performance and Mechanisms

Microbe-derived dissolved organic nitrogen (mDON) can readily induce harmful phytoplankton blooms, and thus, restricting its discharges is necessary. Recently, algae biofilm (AB) has attracted increasing interest for its advantages in nutrient recovery. However, its features in mDON control remain unexplored. Herein, AB's mDON formation and utilization performance, molecular characteristics, and metabolic traits have been investigated, with activated sludge (AS) as the benchmark for comparisons. Comparatively, AB reduced mDON formation by 83% when fed with DON-free wastewater. When fed with AS's effluent, it consumed at least 72% of the exogenous mDON and notably reduced the amount of protein/amino sugar-like compounds. Irrespective of the influent, AB ultimately produced more various unsaturated hydrocarbon and lignin analogues. Redundancy and network analysis highlighted the algal-bacterial synergistic effects exemplified by cross-feeding in reducing mDON concentrations and shaping mDON pools. Moreover, metagenomics-based metabolic reconstruction revealed that cyanobacteria Limnothrix and Kamptonema spp. facilitated mDON uptake, ammonification, and recycling, which supplied the extensive nitrogen assimilatory demand for amino acids, vitamins, and cofactors biosynthesis, and therefore promoted mDON scavenging. Our findings demonstrate that regardless of the secondary or tertiary process, cyanobacteria-dominated AB is promising to minimize bioavailable mDON discharges, which has implications for future eutrophication control.

Removal of pharmaceutical and personal care products (PPCPs) from waterbody using a revolving algal biofilm (RAB) reactor

The occurrence of Pharmaceutical and Personal Care Products (PPCPs) in the aquatic environment has raised concerns due to their accumulation in the ecosystem. This study aims to explore the feasibility of using a Revolving Algal Biofilm (RAB) reactor for PPCPs removal from waterbody. Five model PPCP compounds including ibuprofen, oxybenzone, triclosan, bisphenol A and N, N-diethyl-3-methylbenzamide (DEET) were mixed and added to the culture medium. It shows that PPCP removal efficiencies of the RAB reactor ranged from 70% to 100%. The degradation of PPCPs by the RAB reactor contributed > 90% PPCP removal while < 10% PPCPs removal was due to accumulation in the algal biomass. The nutrients removal performance of the RAB reactor was not affected by exposing to the PPCPs. The extracellular polysaccharides content of the biomass increased when exposing to PPCPs, while the extracellular proteins content remained constant. The Chl a content maintained constant in the PPCPs-treated biomass, but decreased in the biomass without PPCP treatment. It was also found that the microbial consortium of the RAB reactor was enriched with PPCPs degradation microorganisms with the progressing of feeding PPCPs. Collectively, this work demonstrates that the RAB system is a promising technology for removing PPCPs from wastewater.

Analyzing microalgal biofilm structures formed under different light conditions by evaluating cell-cell interactions

Biofilm structure plays an important role in microalgae biofilm-based culture. This work aims to understand microalgal biofilm structures formed under different light conditions. Here, Scenedesmus obliquus was biofilm cultured under the light spectra of white, blue, green, and red, and the photoperiods of 5:5 s, 30:30 min, and 12:12 h (light : dark period). Biofilms were observed with confocal laser scanning microscopes and profilometry, then the porosity and roughness of biofilm were determined. We found that cells under white light formed a heterogeneous biofilm with many voids, high porosity, and roughness. While under red and blue lights, cells formed homogeneous biofilms with low porosity. Biofilm structures formed under different photoperiods were different. The mechanism of forming different biofilm structures under different light conditions was interpreted from the aspect of cell-cell interactions. Moreover, the results revealed that biomass accumulation increased with the increasing biofilm porosity due to the high effective diffusion coefficient.

Stepwise treatment of undiluted raw piggery wastewater, using three microalgal species adapted to high ammonia

A high ammonia concentration and chemical oxygen demand (COD) in piggery wastewater force it to be diluted before conventional microalgal treatment to reduce ammonia toxicity. Incomplete treatment of ammonia and COD in piggery wastewater may cause eutrophication, resulting in algal blooms. This study tried to treat raw piggery wastewater without dilution, using three strains of microalgae (Chlorella sorokiniana, Coelastrella sp. and Acutodesmus nygaardii) that outcompeted other algae under heterotrophic, mixotrophic, and autotrophic conditions, respectively, through adaptive evolution at high ammonia concentration. The three stepwise processes were designed to remove (1) small particles, COD, and phosphorus in the 1st heterotrophic C. sorokiniana cultivation, (2) ammonia and COD in the 2nd mixotrophic Coelastrella sp. cultivation, and (3) the remaining ammonia in the 3rd photoautotrophic A. nygaardii cultivation. To enhance ammonia uptake rate, each algal species were inoculated after 2-day nitrogen starvation. When the N-starved three species were inoculated at each step sequentially at 7 g/L for 2 days, the final phosphorus, COD, and ammonia removal efficiencies were 100% (16.4-0 mg/L), 92% (6820-545 mg/L), 90% (850-81 mg/L) and turbidity (99%) after total 6 days.

Removal of Nitrogen and Phosphorus from Thickening Effluent of an Urban Wastewater Treatment Plant by an Isolated Green Microalga

Microalgae are photosynthetic microorganisms and are considered excellent candidates for a wide range of biotechnological applications, including the removal of nutrients from urban wastewaters, which they can recover and convert into biomass. Microalgae-based systems can be integrated into conventional urban wastewater treatment plants (WW-TP) to improve the water depuration process. However, microalgal strain selection represents a crucial step for effective phytoremediation. In this work, a microalga isolated from the effluent derived from the thickening stage of waste sludge of an urban WW-TP was selected and tested to highlight its potential for nutrient removal. Ammonium and phosphate abatements by microalgae were evaluated using both the effluent and a synthetic medium in a comparative approach. Parallelly, the isolate was characterized in terms of growth capability, morphology, photosynthetic pigment content and photosystem II maximum quantum yield. The isolated microalga showed surprisingly high biomass yield and removal efficiency of both ammonium and phosphate ions from the effluent but not from the synthetic medium. This suggests its clear preference to grow in the effluent, linked to the overall characteristics of this matrix. Moreover, biomass from microalgae cultivated in wastewater was enriched in photosynthetic pigments, polyphosphates, proteins and starch, but not lipids, suggesting its possible use as a biofertilizer.

Innovative microalgae biomass harvesting methods: Technical feasibility and life cycle analysis

In order to ease one of the main challenges of biomass production in wastewater, the harvest stage, this study proposes as main innovations: the comparison of technical and environmental performance of different methods of harvesting biomass which have not been addressed in the literature and the projection of an optimal environmental scenario for biomass harvesting. For this, three harvesting methods were evaluated and compared, namely the gravitational sedimentation (GS) via settling tank, coagulation with tannin followed by gravitational sedimentation (TC/GS), and a biofilm reactor operated in parallel with a settling tank (BR/GS). TC/GS required less time to concentrate the biomass (121.13 g/day); however, the biomass had a higher moisture content (99.02%), which may compromise its direct application for production of most bioproducts and bioenergy, only a dewatering step is recommended. The harvesting methods interfered in biomass characterisation, mainly in carbohydrate content, which was higher in biomass concentrated over time (28-37%) than biomass concentrated in a single day by coagulation (13.8%). The results of the life cycle assessment revealed that in scenarios which included TC/GS methods and the BR/GS presented less environmental impact in relation to only GS. Additionally, the combination of these two methods comprises the best scenario and promises to optimise the harvest of biomass grown in wastewater.

Screening of the dominant Chlorella pyrenoidosa for biofilm attached culture and feed production while treating swine wastewater

This research 12 microalgal species were screened for biofilm attached culture in the treatment of anaerobically digested swine wastewater (ADSW). The influence of ADSW on biomass productivity and removal efficiencies were evaluated using biofilm attached culture with the selected Chlorella pyrenoidosa. The variation of nutritional components from algal cells were further analysed to evaluate the potential applications of C. pyrenoidosa. The results showed that C. pyrenoidosa had the highest tolerance to ADSW, and the highest removal efficiencies for wastewater pollutants were reached when cultured in 5 times diluted ADSW. These test conditions resulted in an algal cell biomass composed of 57.30% proteins, 14.87% extracellular polysaccharide, 3.08% crude fibre, 5.57% crude ash, 2.85% moisture. Amino acids in proteins contained 21.73% essential amino acids and the EAA/NEAA value was 0.64. The essential amino acid score indicates that the selected C. pyrenoidosa could be a good protein source for feed addition.

Innovative hybrid system for wastewater treatment: High-rate algal ponds for effluent treatment and biofilm reactor for biomass production and harvesting

The use of algal biomass still faces challenges associated with the harvesting stages. To address this issue, we propose an innovative hybrid system, in which a biofilm reactor (BR) operates as an algal biomass production and harvesting unit connected to a high-rate algal pond (HRAP), a wastewater treatment unit. BR did not interfered with the biomass chemical composition (protein = 32%, carbohydrates = 11% and total lipids = 18%), with the wastewater treatment (removals efficiency: chemical oxygen demand = 59%, ammonia nitrogen = 78%, total phosphorus = 16% and Escherichia coli = 1 log unit), and did not alter the sedimentation characteristics of the biomass (sludge volume index = 29 mg/L and humidity content = 92%) in the secondary settling tank of the hybrid system. On the other hand, the results showed that this technology achieved a biomass production about 2.6x greater than the conventional system without a BR, and the efficiency of harvesting of the hybrid system was 61%, against 22% obtained with the conventional system. In addition, the BR promoted an increase in the density (~1011 org/m²) and diversity of microalgae in the hybrid system. Chlorella vulgaris was the most abundant species (>60%) from the 4th week of operation until the end of the experiment. Hence, results confirm that the integration of BR into a wastewater treatment plant optimised the production and harvesting of biomass of the hybrid system, making it a promising technology. The importance of economic and environmental analysis studies of BR is highlighted in order to enable its implementation on a large scale.

Inclined algal biofilm photobioreactor (IABPBR) for cost-effective cultivation of lipid-rich microalgae and treatment of seawater-diluted anaerobically digested effluent from kitchen waste with the aid of phytohormones

Previous study has demonstrated that freshwater can be replaced with seawater for dilution of feed to algal production and wastewater treatment, but high harvest cost in suspended-growth systems is still a troublesome limitation for large-scale production. Therefore, a novel inclined algal biofilm photobioreactor (IABPBR) was constructed for algal bioproduct production and treatment of seawater-diluted anaerobically digested effluent (SA) in this study. Fluffy polyester was selected as the best carrier for the algal biofilm among ten discarded materials. With the help of phytohormones, the viability of SDEC-18 was clearly enhanced and an algal biomass productivity of 5.66 g/m²/d was achieved. The SDEC-18 biofilm provided removal capacities of 0.65, 0.25 and 3.31 g/m²/d for TN, TP and COD. Phytohormones clearly enhanced the lipid biosynthesis, with an extraordinary lipid productivity of 3.98 g/m²/d being achieved. Moreover, an automatic harvesting system was designed for the efficient harvesting process during large-scale production.

Removal of total dissolved solids from wastewater using a revolving algal biofilm reactor

Total dissolved solids (TDS) comprising inorganic salts and organic matters are pollutants of concern to aquatic systems and water for human use. This work aimed to investigate the use of revolving algal biofilm (RAB) reactors as a sustainable and environmental friendly method to remove TDS from industrial effluents and municipal wastewaters. The wastewaters contained chloride, sodium, potassium, calcium, magnesium, and sulfate as the major components. The RAB reactors fed with synthetic industrial effluent with high TDS level demonstrated the best algal growth, with the highest TDS removal efficiency (27%) and removal rate (2,783 mg/L-day and 19,530 mg/m² -day). A suspended algal culture system only removed 3% TDS from the same wastewater. The TDS removal by the RAB reactors was considered due to several mechanisms such as absorption by the algae cells, adsorption by extracellular polymeric substance of the biofilm, and/or precipitation. Collectively, this research shows that the RAB reactors can serve as an efficient system in wastewater remediation for TDS removal. PRACTITIONER POINTS: Total dissolved solids (TDS) in wastewater are pollutants of concern. The RAB reactors can remove TDS from various types of wastewater. The RAB reactors removed TDS by adsorbing ions elements such as Cl, Na, K, Ca, Mg, and S. The algal biomass absorbs ions through extracellular polymeric substance.

Cultivation of Chlorella vulgaris in a Light-Receiving-Plate (LRP)-Enhanced Raceway Pond for Ammonium and Phosphorus Removal from Pretreated Pig Urine

Fresh pig urine is unsuitable for microalgae cultivation due to its high concentrations of NH4+-N, high pH and insufficient magnesium. In this study, fresh pig urine was pretreated by dilution, pH adjustment, and magnesium addition in order to polish wastewater and produce microalgae biomass. Chlorella vulgaris was cultured in an in-house-designed light-receiving-plate (LRP)-enhanced raceway pond to treat the pretreated pig urine in both batch and continuous mode under outdoor conditions. NH4+-N and TP in wastewater were detected, and the growth of C. vulgaris was evaluated by chlorophyll fluorescence activity as well as biomass production. Results indicated that an 8-fold dilution, pH adjusted to 6.0 and MgSO4·7H2O dosage of 0.1 mg·L−1 would be optimal for the pig urine pretreatment. C. vulgaris could stably accumulate biomass in the LRP-enhanced raceway pond when cultured by both BG11 medium and the pretreated pig urine. About 1.72 g·m−2·day−1 of microalgal biomass could be produced and 98.20% of NH4+-N and 68.48% of TP could be removed during batch treatment. Hydraulic retention time of 7-9d would be optimal for both efficient nutrient removal and microalgal biomass production during continuous treatment.

Enhanced nutrients enrichment and removal from eutrophic water using a self-sustaining in situ photomicrobial nutrients recovery cell (PNRC)

Nutrients removal and recovery from surface water are attracting wide attention as nutrients contamination can cause eutrophication even threaten human health. In this study, a novel in-situ photomicrobial nutrient recovery cell (PNRC) was developed, which employed the self-generated electric field to drive nutrient ions to migrate and subsequent recovery as microalgae biomass. At an external resistance of 200 Ω, the current density of the PNRC reactor reached 2.0 A m^-2, more than 92% of ammonium nitrogen (NH₄⁺-N), nitrate nitrogen (NO₃^--N), and total phosphorus (TP) were separated from eutrophic water, which represented <0.19 mg L^-1 of NH₄⁺-N, <0.23 mg L^-1 of NO₃^--N, <0.02 mg L^-1 of TP were left in the eutrophic water effluent. Meanwhile these separated NH₄⁺-N, NO₃^--N, and TP were highly enriched in the cathode and anode chambers, and further removed from the system with the removal efficiencies of 91.8%, 90.6%, and 94.4%. The analysis of microbial communities unraveled that high nitrate removal was attributed to the abundant denitrifying bacteria (Thauera, Paracoccus, Stappia, and Azoarcus). The removal of ammonia was attributed to the algae assimilation (69.3%) and nitrification process (22.5%), and the phosphorus removal was mainly attributed to C. vulgaris. The preliminary energy balance analysis indicated that the electricity generation and biodiesel production could achieve energy neutrality theoretically, further demonstrating the huge potential of the PNRC system in cost-effective nutrients recovery from eutrophic water.

Review on biological wastewater treatment and resources recovery: attached and suspended growth systems

The treatment of wastewater for reuse is a potential solution to meet ever increasing urban, industrial, agricultural, and environmental demands across the world, where clean water availability is scarce. There are several traditional wastewater treatment processes that offer varying degrees of effectiveness in addition to presenting environmental, economic, and social disadvantages. Development of promising and inexpensive technologies to provide the reusable water in needful amounts using wastewaters as a cheap source of key nutrients and organic matter is required. Wastewater treatment by biological methods is becoming more important in the light of recovering value-added plant nutrients, heavy metals, biosolids, and bioenergy resources. Different types of solid contaminants in effluents can be removed simultaneously by pure cultures or mixed microbial consortia. Based on the structural organization of microbial biomass, biological treatment systems are classified into two types: dispersed growth system and attached growth system. Biological treatment methods associated with fixed-film growth have been recognized as highly effective and more energy efficient than suspended growth systems. This review discusses the recent breakthroughs in advanced biological wastewater treatment using both the systems, and also focuses on key energetic resources recovery driven by biological technologies.

Microalgae wastewater treatment: Biological and technological approaches

Current global environmental issues raise unavoidable challenges for our use of natural resources. Supplying the human population with clean water is becoming a global problem. Numerous organic and inorganic impurities in municipal, industrial, and agricultural waters, ranging from microplastics to high nutrient loads and heavy metals, endanger our nutrition and health. The development of efficient wastewater treatment technologies and circular economic approaches is thus becoming increasingly important. The biomass production of microalgae using industrial wastewater offers the possibility of recycling industrial residues to create new sources of raw materials for energy and material use. This review discusses algae-based wastewater treatment technologies with a special focus on industrial wastewater sources, the potential of non-conventional extremophilic (thermophilic, acidophilic, and psychrophilic) microalgae, and industrial algae-wastewater treatment concepts that have already been put into practice.

Adsorption behaviors of Cu2+, Zn2+ and Cd2+ onto proteins, humic acid, and polysaccharides extracted from sludge EPS: Sorption properties and mechanisms

To clarify the adsorption behaviors of typical heavy metals onto sludge extracellular polymeric substances (EPS), the adsorption capacities and mechanisms, as well as the contributions of the different EPS components (proteins, humic acids and polysaccharides), to the adsorption of Zn²⁺, Cu²⁺ and Cd²⁺ were separately explored. Overall, proteins exhibited a relatively high adsorption capacity for the three metals ions, followed by humic acid, whereas least for polysaccharides. The adsorption of Cu²⁺ and Cd²⁺ onto proteins, humic acid and polysaccharides fit well to the Freundlich isotherm, whereas Langmuir model was the best fit for Zn²⁺ bindings onto polysaccharides/humic acid. The binding of Cu²⁺, Zn²⁺ and Cd²⁺ onto the three EPS components was exothermically favorable, and significant electrostatic interactions were observed for the heavy metals sorption onto humic acid and proteins. In addition, the effect of metal ions sorption on the spectrum of the proteins, polysaccharides and humic acid was also explored.

A novel algal biofilm photobioreactor for efficient hog manure wastewater utilization and treatment

This study developed a high-efficiency algal biofilm photobioreactor for microalgae by designing a special array of curtain membrane components. This paper also discusses the growth and nutrient composition of Chlorella vulgaris, and hog manure wastewater utilization and purification. It was found that after about 5 days of culture, the biomass of C. vulgaris on the membrane could reach as high as 7.37 g/m2 and the algae were easily harvested by mechanical scraping. The lipid content of C. vulgaris on the membrane structure was 10.17% while the lipid content of the algae in suspension was 14.29%. The light intensity showed a significant effect on the fatty acid composition. The C. vulgaris grew very well, and achieved deep purification of the hog manure wastewater; the COD, TP, TN, and NH4+-N removal rates reached 95.67%, 64.40%, 69.55%, and 91.24%, respectively.

Quantitative Criterion to Predict Cell Adhesion by Identifying Dominant Interaction between Microorganisms and Abiotic Surfaces

Cell adhesion is ubiquitous and plays an important role in various scientific and engineering problems. Herein, a quantitative criterion to predict cell adhesion was proposed by identifying the dominant interaction between microorganisms and abiotic surfaces. According to the criterion, the dominant interaction in cell adhesion could be identified as a Lewis acid-base (AB) interaction or electrostatic (EL) interaction via comparison of two expressions containing the electron-donor characteristics of the microorganism (γ_mv^-) and abiotic surface (γ_sv^-) and their ζ potentials (ζ_m, ζ_s). The results revealed that when dominated by the AB interaction, adhesion would decrease with increasing [Formula: see text]. However, when the EL interaction was dominant, adhesion would decrease with increasing (ζ_m + ζ_s)². We have verified the criterion based on the adhesion of microalgae, bacteria, and fungi onto various surfaces obtained via our experiments and available in literature studies. The results demonstrated that the criterion had important implications in the prediction of cell adhesion in various applications.