Microalgal Wastewater Treatment Research Articles

Intensified microalgae production and development of microbial communities on suspended carriers and municipal wastewater

Wastewater represents an alternative source of nutrients in which to grow microalgae, whilst improving the quality of the wastewater, and reducing the downstream treatment required. However, commercialisation of microalgal cultures for such duties faces a number of challenges, predominantly high cost and low productivity. Suspended-solid reactors (ssPBR) can reduce the operational costs, while promoting attached and suspended microalgae growth. In the present study, a novel approach was developed by integrating microalgal wastewater treatment with carrier systems to favour the growth of both attached and suspended cells of T. obliquus. This study found that T. obliquus was able to uptake nutrients from municipal wastewater, achieving removals of 99.3–99.9 % NH3-N, 54.5–88.5 % PO43− and 92.8–94.5 % DTC. The addition of a 12.5 % volumetric fill ratio of carriers in ssPBRs produced higher microalgal cell productivity (1.2·106 ± 2.5·105 cell ml−1 d−1) than the control (4.3·105 ± 2.8·105 cell ml−1 d−1). MinION nanopore sequencing was conducted to assess the impact of microalgal and carrier treatment on wastewater bacterial communities. It was found not only that bacterial communities had changed after the treatment but also the ones attached differed from the ones suspended. Untreated wastewater was characterised by the abundance of sewer bacteria genera such as Aliarcobacter and Arcobacter, whilst, after treatment, microbial communities were characterised by the presence of photosynthetic freshwater (Limnococcus, Stanieria) and bioremediation-like bacteria genera (Pseudomonas, Rheinheimera). In conclusion, the addition of 12.5 % fill carrier ratio increased microalgal productivity, while stimulating changes in the algal microbiome, and creating distinctly different populations in the free and attached environments.

Unveiling significant roles of phytohormone 6-benzylaminopurine in empowering Phaeodactylum tricornutum for high-salinity wastewater treatment and bioresource recovery

High-salinity presents significant challenges in microalgal wastewater treatment and bioresource recovery due to salinity stress. This study explored the use of salt-tolerant microalgae in conjunction with phytohormone regulation. 1 µM 6-benzylaminopurine increased the biomass of Phaeodactylum tricornutum by 38.3 % and enhanced lipid production by 36.8 %. 6-benzylaminopurine significantly improved the removal of inorganic carbon, total nitrogen, and total phosphorus by 85.2 %, 27.4 %, and 31.9 %. Specifically, 6-benzylaminopurine improved K+ transportation by 71.0 %, increased the activity of Ca2+ transport ATPase and Ca2+ sensors by 49.0 %–83.0 %, optimized osmotic balance, and alleviated salt-induced damage. The contents of proline and extracellular polymers increased by 34.8 % and 35.5 %. A 38.4 % reduction in reactive oxygen species indicated that high-salinity stress was mitigated. The analysis of Sustainable Development Goals showed a 56.2 % improvement in Affordable and Clean Energy. Overall, these findings further highlighted the promising application of the phytohormone 6-benzylaminopurine in microalgal high-salinity wastewater treatment and lipid production.

Amide groups within polystyrene accelerates tetracycline removal in a continuous advanced microalgal treatment system

Livestock effluents are challenging to be treated owing that antibiotics and microplastics are untargeted for most biological technologies. As far, microalgal wastewater treatment is recognized as an effective technique for dealing with. In this study, a continuous-flow system was conducted over 45 days to evaluate the effectiveness of Chlamydomonas sp. JSC4 in removing tetracycline (TCH) under the influence of polystyrene (PS). It shows that PS significantly enhanced the dissipation efficiency of TCH from livestock effluents, and 9.83 % TCH removal was increased under 5 mg/L of both TCH and PS exposure. Meanwhile, higher microalgal bioactivity was a significant factor in achieving desirable pollutants removal efficiency, as 87.14 % microalgal biomass was improved owing to reduction of oxidative stress and augmentation of photosynthesis. Importantly, the pivotal active sites, NH2 and CO, were rapidly covered via π-π interactions and hydrogen bonds during adsorption process between TCH and PS, accounting for mitigation of TCH-PS complexes toxicity and improvement of microalgal ribosome metabolism. Additionally, co-exposure to TCH and PS resulted in maximum lipids (0.57 g/L) and energy (20.79 kJ/L) production, further encouraging a fantastic vision for the tertiary process of livestock effluents via advanced microalgal treatment.

Intensive Microalgal Cultivation and Tertiary Phosphorus Recovery from Wastewaters via the EcoRecover Process.

Mixed community microalgal wastewater treatment technologies have the potential to advance the limits of technology for biological nutrient recovery while producing a renewable carbon feedstock, but a deeper understanding of their performance is required for system optimization and control. In this study, we characterized the performance of a 568 m3·day-1 Clearas EcoRecover system for tertiary phosphorus removal (and recovery as biomass) at an operating water resource recovery facility (WRRF). The process consists of a (dark) mix tank, photobioreactors (PBRs), and a membrane tank with ultrafiltration membranes for the separation of hydraulic and solids residence times. Through continuous online monitoring, long-term on-site monitoring, and on-site batch experiments, we demonstrate (i) the importance of carbohydrate storage in PBRs to support phosphorus uptake under dark conditions in the mix tank and (ii) the potential for polyphosphate accumulation in the mixed algal communities. Over a 3-month winter period with limited outside influences (e.g., no major upstream process changes), the effluent total phosphorus (TP) concentration was 0.03 ± 0.03 mg-P·L-1 (0.01 ± 0.02 mg-P·L-1 orthophosphate). Core microbial community taxa included Chlorella spp., Scenedesmus spp., and Monoraphidium spp., and key indicators of stable performance included near-neutral pH, sufficient alkalinity, and a diel rhythm in dissolved oxygen.

Environmental impact assessment via life cycle analysis on ultrafiltration membrane fabricated from polyethylene terephthalate waste to treat microalgal cultivation wastewater for reusability

The current study had conducted the life cycle analysis (LCA) to assess the environmental impact of microalgal wastewater treatment via an integrated membrane bioreactor. The functional unit selected for this analysis was 1 kg of treated microalgal wastewater with contaminants eliminated by ultrafiltration membrane fabricated from recycled polyethylene terephthalate waste. Meanwhile, the applied system boundary in this study was distinguished based on two scenarios, namely, cradle-to-gate encompassed wastewater treatment only and cradle-to-cradle which included the reutilization of treated wastewater to cultivate microalgae again. The environmental impacts and hotspots associated with the different stages of the wastewater treatment process had clearly elucidated that membrane treatment had ensued the highest impact, followed by microalgal harvesting, and finally cultivation. Among the environmental impact categories, water-related impact was found to be prominent in the following series: freshwater ecotoxicity, freshwater eutrophication and marine ecotoxicity. Notably, the key performance indicator of all environmental impact, i.e., the global warming potential was found to be very much lower at 2.94 × 10−4 kg CO2 eq as opposed to other literatures reported on the LCA of wastewater treatments using membranes. Overall, this study had proffered insights into the environmental impact of microalgal wastewater treatment and its stimulus for sustainable wastewater management. The findings of this study can be instrumental in making informed decision for optimizing microalgal wastewater treatment and reutilization assisted by membrane technology with an ultimate goal of enhancing sustainability.

Utilization of native Chlorella strain in laboratory-scale raceway reactor for synthetic wastewater treatment: A study in batch and continuous modes with multi-substrate modeling

Despite of the possibility to include microalgae in civil wastewater treatment process, the practice is still not common due to the lack of available instruments to implement it. In this study, a straightforward comprehensive approach for dealing with microalgal wastewater treatment involving an original kinetic model is proposed. A first set of batch cultures of a native strain of Chlorella was firstly carried out to obtain the kinetic parameters: maximum growth factor (μmax) and half-saturation constant (Ks), for each limiting nutrient. Maximum growth factor values of 0.0279 for PO43−, 0.0319 h−1 for NH4+, 0.0352 h−1 for glucose, and 0.0263 h−1 for the overall medium were found. Regarding the Ks, values of 1.08 mg L−1, 27.70 mg L−1, 1.34 mg L−1, were found for PO43−, NH4+ and glucose respectively, and a value of 2.8 % of the total nutrients for the overall medium. These parameters were used to set a multi-substrate kinetic model able to predict the growth in batch and in continuous operation within a laboratory scale raceway reactor. The removal capabilities of the microalgae for each addressed pollutant were evaluated in a batch system and in a continuous system at dilution rates of 0.0025, 0.005, 0.01 and 0.015 h−1. This comprehensive approach represents a significant step towards addressing the continuous treatment of wastewater utilizing microalgae.

Ultrafiltration membrane fabricated from polyethylene terephthalate plastic waste for treating microalgal wastewater and reusing for microalgal cultivation

Current study had made a significant progress in microalgal wastewater treatment through the implementation of an economically viable polyethylene terephthalate (PET) membrane derived from plastic bottle waste. The membrane exhibited an exceptional pure water flux of 156.5 ± 0.25 L/m2h and a wastewater flux of 15.37 ± 0.02 L/m2h. Moreover, the membrane demonstrated remarkable efficiency in selectively removing a wide range of residual parameters, achieving rejection rates up to 99%. The reutilization of treated wastewater to grow microalgae had resulted in a marginal decrease in microalgal density, from 10.01 ± 0.48 to 9.26 ± 0.66 g/g. However, this decline was overshadowed by a notable enhancement in lipid production with level rising from 181.35 ± 0.42 to 225.01 ± 0.11 mg/g. These findings signified the membrane's capacity to preserve nutrients availability within the wastewater; thus, positively influencing the lipid synthesis and accumulation within microalgal cells. Moreover, the membrane's comprehensive analysis of cross-sectional and surface topographies revealed the presence of macropores with a highly interconnected framework, significantly amplifying the available surface area for fluid flow. This exceptional structural attribute had substantially contributed to the membrane's efficacy by facilitating superior filtration and separation process. Additionally, the identified functional groups within the membrane aligned consistently with those commonly found in PET polymer, confirming the membrane's compatibility and efficacy in microalgal wastewater treatment.

Immobilized microalgal system: An achievable idea for upgrading current microalgal wastewater treatment.

Efficient wastewater treatment accompanied by sustainable "nutrients/pollutants waste-wastewater-resources/energy nexus" management is acting as a prominent and urgent global issue since severe pollution has occurred increasingly. Diverting wastes from wastewater into the value-added microalgal-biomass stream is a promising goal using biological wastewater treatment technologies. This review proposed an idea of upgrading the current microalgal wastewater treatment by using immobilized microalgal system. Firstly, a systematic analysis of microalgal immobilization technology is displayed through an in-depth discussion on why using immobilized microalgae for wastewater treatment. Subsequently, the main technical approaches employed for microalgal immobilization and pollutant removal mechanisms by immobilized microalgae are summarized. Furthermore, from high-tech technologies to promote large-scale production and application potentials in diverse wastewater and bioreactors to downstream applications lead upgradation closer, the feasibility of upgrading existing microalgal wastewater treatment into immobilized microalgal systems is thoroughly discussed. Eventually, several research directions are proposed toward the future immobilized microalgal system for microalgal wastewater treatment upgrading. Together, it appears that using immobilization for further upgrading the microalgae-based wastewater treatment can be recognized as an achievable alternative to make microalgal wastewater treatment more realistic. The information and perspectives provided in this review also offer a feasible reference for upgrading conventional microalgae-based wastewater treatment.

Nutrient conservation achieved through mixing regime improves microalgal wastewater treatment and diminishes the net environmental impact

Operational mode of photobioreactor (PBR) play pivotal role in environmentally benign wastewater treatment. In this context, there is wider knowledge gap in decision making for sustainable microalgae PBR operation with least environmental impact. Therefore, the present work utilized two operational modes, aeration and mechanical mixing (non-aeration), for comparative evaluation of their impacts on nutrient removal, microalgae: bacteria (M:B) population dynamics, and performance along with environmental impact. The experiments initiated with dominant M:B inoculation ratio (60:40), demonstrated higher M:B ratio (78:21) with mixing regime, as essential nutrients (dissolved inorganic carbon and ammoniacal nitrogen) were conserved within the wastewater. On the other hand, lower M:B ratio (36:63) was obtained during aeration regime, as these nutrients were transformed into CO2 and NH3 and emitted to the environment. The nutrient conservation mechanism within mixing regime enhanced microalgal growth by 30 %, metal removal by 14–59 %, and exhibited carbon negative global warming potential (-0.0451 kgCO2 eqm−3), along with overall non-negative environmental impact. In contrast, aeration strategy showed net negative environmental impact with reduced contaminant removal potential. Overall, this study reveals a previously overlooked yet significant contribution of nutrient conservation achieved through mixing regime for holistic wastewater treatment.

Effect of free ammonia shock on Chlorella sp. in wastewater: Concentration-dependent activity response and enhanced settleability

The unstable microbial activity and unsatisfactory settling performance impede the development and implementation of microalgal wastewater treatment, especially in high-ammonium wastewater in the presence of free ammonia (FA). The shock of FA due to the nutrient fluctuation in wastewater was demonstrated as the primary stress factor suppressing microalgal activities. Recent study has clearly revealed the inhibition mechanism of FA at a specific high level (110.97 mg/L) by inhibiting the genetic information processing, photosynthesis, and nutrient metabolism. However, the effects of various FA shock concentrations on microalgal activities and settling performance remain unknown, limiting the wastewater bioremediation efficiencies improvement and the process development. Herein, a concentration-dependent shock FA (that was employed on microalgae during their exponential growth stages) effect on microalgal growth and photosynthesis was observed. Results showed that the studied five FA shock concentrations ranging from 25 to 125 mg/L significantly inhibited biomass production by 14.7–57.0%, but sharp reductions in photosynthesis with the 36.0–49.0% decreased Fv/Fm values were only observed when FA concentration was above 75.0 mg/L. On the other hand, FA shock enhanced microalgal settling efficiency by 12.8-fold, which was believed to be due to the stimulated intra- and extracellular protein contents and thereby the enhanced extracellular polymer substances (EPS) secretion. Specifically, FA shock induced 40.2 ± 2.3% higher cellular protein content at the cost of the decreased carbohydrates (22.6 ± 1.3%) and fatty acid (39.0 ± 0.8%) contents, further improving the protein secretion by 1.21-fold and the EPS production by 40.2 ± 2.3%. These FA shock-induced variations in intra- and extracellular biomolecules were supported by the up-regulated protein processing and export at the assistance of excessive energy generated from fatty acid degradation and carbohydrates consumption. In addition, FA shock significantly decreased the biomass nutritional value as indicated by the 1.86-fold lower essential amino acid score and nearly 50% reduced essential to non-essential amino acids ratio, while slightly decreased the biodiesel quality. This study is expected to enrich the knowledge of microalgal activities and settling performance in response to fluctuant ammonium concentrations in wastewater and to promote the development of microalgal wastewater treatment.

Extra benefit of microalgae in raw piggery wastewater treatment: pathogen reduction

BackgroundMonitoring microbial communities especially focused on pathogens in newly developed wastewater treatment systems is recommended for public health. Thus, we investigated the microbial community shift in a pilot-scale microalgal treatment system for piggery wastewater.ResultsMicroalgae showed reasonable removal efficiencies for COD and ammonia, resulting in higher transparency of the final effluent. Metagenome and microbial diversity analyses showed that heterotrophic microalgal cultivation barely changed the bacterial community; however, the mixotrophic microalgal cultivation induced a sudden change. In addition, an evaluation of risk groups (RGs) of bacteria showed that raw piggery wastewater included abundant pathogens, and the microalgal treatment of the raw piggery wastewater decreased the RG2 pathogens by 63%. However, co-cultivation of microalgae and the most dominant RG2 pathogen, Oligella, showed no direct effects between them.ConclusionsThus, a microbial interaction network was constructed to elucidate algae-bacteria interrelationships, and the decrease in Oligella was indirectly connected with microalgal growth via Brevundimonas, Sphingopyxis, and Stenotrophomonas. In a validation test, 3 among 4 connecting bacterial strains exhibited inhibition zones against Oligella. Therefore, we showed that microalgal wastewater treatment causes a decrease in RG2 bacteria, which is an indirect impact of microalgae associated with bacteria.Graphical 9xuCqXStUBwsH8dUwtqkoYVideo abstract

Improving microalgal tolerance to high ammonia with simple organic carbon addition for more effective wastewater treatment

Due to ammonia toxicity in microalgal treatment systems, wastewaters with excessive ammonia require pre-treatment, either dilution or chemical stripping, but this can be costly. Alternatively, the addition of organic carbon may help to alleviate toxicity. This study investigated effects of glucose addition on toxicity in three microalgal species. Glucose reduced toxicity at ammonia concentrations from 50 to 1000 mg L−1, in all species. Growth rate, cell count and biovolume significantly increased (p < 0.01) with glucose, at all ammonia concentrations. Carbon to nitrogen ratio (C:N) was important for maximising tolerance, varying with species, ammonia concentration and parameter measured. For Chlorella sorokiniana, the highest total biovolume yield (2.3 × 104 ± 1.3 × 103 μm−3 mL−1) was achieved at 25 mg L−1 and C:N = 5, for Coelastrum sp., (1.0 × 104 ± 0.8 × 103 μm−3 mL−1) it was achieved at 750 mg L−1 and C:N = 9, and for Desmodesmus communis (6.9 × 107 ± 5.2 × 106 μm−3 mL−1) it was achieved at 1000 mg L−1 and C:N = 5. When grown on food-waste centrate, effective quantum yield, light absorption, growth rate, biomass yield and nutrient removal were all inhibited at concentrations between 100 and 500 mg L−1. However, the addition of glucose at C:N = 1, or 5, alleviated ammonia toxicity, resulting in significantly higher (p < 0.01) biomass and nutrient removal. The simple addition of glucose was effective at reducing ammonia toxicity and improving microalgal wastewater treatment in both defined medium and centrate at lab-scale. Further research is needed to assess effectiveness at scale for improved wastewater treatment.

Adsorption of sulfamethoxazole via biochar: The key role of characteristic components derived from different growth stage of microalgae

Converting microalgal biomass residues into biochar (BC) after microalgal wastewater treatment is a popular approach that can produce an adsorbent to treat refractory organic pollutants. Moreover, the adsorption efficiency via BC is closely associated with the surface morphology, which may be determined by the composition of the microalgal biomass. However, the intrinsic relationship and advanced mechanism between the adsorption efficiency and microalgal composition have not been thoroughly investigated. In this work, four microalgal BCs were prepared from Chlamydomonas sp. QWY37 (CBC) after collection from four different growth stages of microalgal biomass during wastewater treatment. The adsorption performance for sulfamethoxazole indicates that the CBC collected in the mid-log phase (CBCL-M) possessed the best adsorption capacity (287.89 mg/g) owing to the higher decomposition of the microalgal cellular protein concentration (70%). Meanwhile, a higher protein content contributed to the largest specific surface area (42.16 m2/g), maximum pore volume (0.037 cm3/g) and abundant surface functional groups of the CBCL-M. Furthermore, based on the theoretical calculation of the structural analysis, the adsorption mechanism was a multilayer adsorption process in accordance with the Freundlich isotherm. Additionally, the strong hydrogen bond, electron donor-acceptor interaction and electrostatic attraction were the main adsorption mechanisms due to the carboxyl/ester functional groups. The results of this research provide a novel perspective on the reasonable harvest of microalgal biomass for BC fabrication and large-scale implementation of microalgal BC in future applications.

Optimization, upscaling and kinetic study of famine technique in a microalgal biofilm-based photobioreactor for nutrient removal

Microalgal wastewater treatment systems are promoted as promising, while harvesting costs, low removal efficiency, and long process time are major obstacles. The present study aims to introduce a comprehensive solution to overcome the difficulties by combining two methods of depletion and biofilm in the culture of Scenedesmus sp. using synthetic wastewater. For this purpose, two factors of depletion periods (one, two, three, and five days) and types of depletion (nitrogen, phosphorus, and both) were optimized by Taguchi design for the wastewater nutrient removal rate in lab-scale. The analysis of factors showed that a five-day complete depletion of nitrogen and phosphorus had the most significant effect on the removal of nitrogen compounds and phosphate, respectively. Optimization of factors led to 35, 8, 28 percent increases in ammonium, nitrate, and phosphate removal efficiencies, respectively and about 50 percent decrease in the process time in flasks. Lab-scale results were validated in cylindrical photobioreactors with external recycling (CPBERs) that achieved 73.2, 76.6, and 65.3 percent in ammonium, nitrate, and phosphate removal efficiencies, respectively. Finally, the comparative kinetic study of starved and non-starved processes led to a remarkable change in concentration dependency from first- to second-order after depletion. The optimized system that was provided can be of benefit for further researches in this area.

Year-long performance assessment of an on-site pilot scale (100 L) photobioreactor on nutrient recovery and pathogen removal from urban wastewater using native microalgal consortium

The study was carried out as part of the Indo-Dutch collaboration project to ascertain the efficacy of the algal system for the treatment of urban wastewater. The study was done at Barapullah drain in New Delhi, using a pilot-scale (100 L) bubble column microalgae photobioreactor (PBR). The year-long study was intended to find the impact of seasonality coupled with varying hydraulic retention times (HRTs) on the PBR performance in terms of nutrient recovery, microbial contamination reduction, biomass productivity, and theoretical biomethane potential.To begin with, native microalgae consortium was enriched and cultivated in PBR directly on the Barapullah drain wastewater at the drain site. After achieving maximum recovery of nutrients in the batch mode, the PBR was operated in continuous mode at HRTs ranging from 1 to 3 days during summer, while 2–3 days during monsoon, autumn, and winter. The maximum and minimum biomass productivity obtained was 260 mg L−1 d−1 at the HRT of 1 day during summer and 77 mg L−1 d−1 at the HRT of 2 days during winter. At peak overall PBR performance at HRT of 2 days, the nutrient removal rate was 37.2 ± 6.2 mgCOD L−1 d−1, 39.3 ± 6 mgN L−1 d−1, and 4.7 ± 0.7 mgP L−1 d−1. Nearly 5 log removal of total and faecal coliform was obtained during summer and monsoon. However, the overall performance reduced during winters. The natural sedimentation of grown biomass achieved 81–95% of biomass settling at different HRTs. The areal footprint of the PBR is 1.42 m2 KLD−1, which was significantly lower than other pilot-scale microalgal wastewater treatment technologies. The obtained results at this lower HRT (2 days) even under non-optimized process parameters represent vital improvements over earlier reports with significantly higher HRTs. Results thus highlight the feasibility and scalability of the technology.

Thermophilic biogas production from microalgae-bacteria aggregates: biogas yield, community variation and energy balance

Biogas production through anaerobic mesophilic digestion is the most straightforward biofuel production route integrated into microalgae-bacteria wastewater treatment plants. Improvement of this biofuel route without adding pretreatment units is possible through the temperature increase. This paper presents a comprehensive evaluation of the transitory effect of different temperatures (35 °C and 55 °C) and hydraulic retention times (HRT) of 15 and 30 d on the long-term methane production using non-pretreated microalgae-bacteria aggregates as a feedstock. The thermophilic transition from mesophilic inoculum adapted to microalgae-bacteria aggregate increased 1.7-fold the methane production (0.41 m3CH4 kgVS−1) at HRT of 30 d. A substantial decrease in the microbial community’s diversity present in the anaerobic reactor was observed when thermophilic conditions were applied, explaining the long adaptation period needed. The increase of the operative temperature condition promotes changes in the dominance pathway of methanogenesis from hydrogenotrophic to acetolactic. The energy balance assessment showed a positive net energy ratio when the digester was operated at an HRT of 30 d. A maximum net energy ratio of 1.5 was achieved at mesophilic temperature. This study demonstrated, based on experimental data, that microalgal digestion with an HRT of 30 d favors energy self-sustainability in microalgal wastewater treatment plants.

Trade-offs between effluent quality and ammonia volatilisation with CO2 augmented microalgal treatment of anaerobically digested food-waste centrate

Diversion of food waste from landfill disposal to waste-to-energy facilities has become both an environmentally and economically viable option to support the circular bioeconomy. However, the liquid centrate produced during anaerobic digestion is high in total ammonia, with concentrations ~2000 g m−3, and can release gaseous emissions, including ammonia, methane, CO2 and nitrous oxide, to the atmosphere. Further treatment is required before discharge to sewer, or to the environment. Microalgal wastewater treatment systems augmented with CO2 offer a promising and cost-effective treatment solution for reducing both total ammonia concentrations and ammonia volatilisation. In this study, we investigate the effects of augmenting CO2 on nutrient removal and specifically nitrogen losses, as well as biomass productivity under two difference hydraulic retention times (HRT). Both CO2 addition and HRT affect nitrogen losses, with the percentage removal of total ammonia significantly lower (p < 0.01) when CO2 was added to the treatments, while increased HRT significantly increased (p < 0.05) total ammonia percentage removal. Total nitrogen budgets showed significantly lower (p < 0.01) abiotic nitrogen losses from the system when CO2 was added to the culture but at the expense of effluent quality. Both total suspended solids and volatile suspended solids significantly increased (p < 0.01) under longer HRT (8 days), with CO2 addition, while chlorophyll-a biomass significantly increased (p < 0.01) on longer HRT, regardless of CO2 addition. These results demonstrate that, while CO2 augmentation helped to mitigate ammonia losses to atmosphere, the trade-off was poorer effluent quality. Coupling CO2 augmentation with longer HRT increased biomass production and nutrient removal efficiency. This study provides an insight into how simple operational changes can alleviate some of the trade-offs between atmospheric losses and effluent quality. However, in order to manage the trade-off between reduced atmospheric losses and poorer effluent quality, further optimisation of the operation of the microalgal system treating food-waste centrate is required.

CHROMIUM REMOVAL FROM TANNERY WASTEWATER: A REVIEW

Tanning process generates high strength wastewater containing heavy metals, nutrients, organic and inorganic contaminants, which may adversely affect public health and the environment. The wastewater contains considerable amounts of heavy metals including Cr(VI) which is carcinogenic, mutagenic and teratogenic, and persistent in the environment. Several physico-chemical treatment approaches were employed in tannery wastewater treatment and proved to considerably reduce the level of toxic Cr and other pollutants to low concentrations. Despite the capabilities of physico-chemical treatment methods in treating high concentrations of toxic effluents, they are associated with setbacks including low removal efficiencies, high cost of chemicals, high energy requirement as well as low nutrients removal from the wastewater stream. Microalgal wastewater treatment systems can play an important role in bioremediation of tannery effluent and are considered as low-cost, efficient treatment alternatives that can potentially remove organic and inorganic contaminants, heavy metals, and possibly reduce the toxic Cr (VI) to a much less toxic Cr (III), especially when coupled with activated carbon.Keywords: microalgae, effluent, chromium, activated sludge, absorption, heavy metals

A Feasibility Study of Wastewater Treatment Using Domestic Microalgae and Analysis of Biomass for Potential Applications

Water scarcity and emerging demands for renewable energy have increased concerns about energy security and advanced wastewater treatment, and microalgae have emerged as promising candidates to solve these problems. This study assesses the feasibility of microalgal wastewater treatment, and the utilization of the resulting microalgal biomass, as a renewable energy source. We cultured four selected microalgal species in filtered wastewater collected from the municipal treatment facility in Daegu, Republic of Korea. We measured nutrient consumption, growth rate, and physicochemical properties during cultivation, then analyzed the biomass for biochemical composition, ultimate analysis, proximate analysis, and biodiesel and lubricant properties, to estimate its potential applications. Desmodesmus sp. KNUA024 emerged as the most promising strain, removing 99.10% of ammonia nitrogen, 91.31% of total nitrogen, and 95.67% of total phosphate. Its biomass had a calorific value of 19.5 MJ kg−1, similar to terrestrial plants. α-linolenic acid was the most abundant polyunsaturated fatty acid (PUFA; 54.83%). Due to its PUFA content, Desmodesmus sp. KNUA024 also had a high iodine value, indicating its potential for use as a bio-lubricant. Therefore, Desmodesmus sp. KNUA024 shows promise for wastewater treatment, energy, and industrial applications.

Enhanced and Balanced Microalgal Wastewater Treatment (COD, N, and P) by Interval Inoculation of Activated Sludge.

Although chemical oxygen demand (COD) is an important issue for wastewater treatment, COD reduction with microalgae has been less studied compared to nitrogen or phosphorus removal. COD removal is not efficient in conventional wastewater treatment using microalgae, because the algae release organic compounds, thereby finally increasing the COD level. This study focused on enhancing COD removal and meeting the effluent standard for discharge by optimizing sludge inoculation timing, which was an important factor in forming a desirable algae/bacteria consortium for more efficient COD removal and higher biomass productivity. Activated sludge has been added to reduce COD in many studies, but its inoculation was done at the start of cultivation. However, when the sludge was added after 3 days of cultivation, at which point the COD concentration started to increase again, the algal growth and biomass productivity were higher than those of the initial sludge inoculation and control (without sludge). Algal and bacterial cell numbers measured by qPCR were also higher with sludge inoculation at 3 days later. In a semi-continuous cultivation system, a hydraulic retention time of 5 days with sludge inoculation resulted in the highest biomass productivity and N/P removal. This study achieved a further improved COD removal than the conventional microalgal wastewater treatment, by introducing bacteria in activated sludge at optimized timing.