Algal Wastewater Treatment System Research Articles

Single-step mixotrophic algal wastewater treatment: Microbial assessment of effluent

Viability of a single-step mixotrophic algal wastewater treatment (A-WWT) system in delivering discharge-quality effluent has been previously demonstrated. This report presents inactivation performance of the A-WWT system and compares it with that of high-rate algal ponds, activated sludge, and membrane bioreactors. Log reduction per unit energy input/volume of wastewater by the A-WWT system is shown to range 6.4–14.6 m3/kWh, while that in the above alternatives ranged 1.3–3.5 m3/kWh. Pathogenicity and virulence of the algal effluent and the potential for formation of disinfection byproducts (DBPs) under chlorination are discussed. Concentrations of seven of the common nitrogenous DBPs in the algal effluent were <50 ng/L.

Algal wastewater treatment integrated with carbon adsorption and ozonation for water reclamation: Multi-criteria comparison with conventional pathways

Our previous reports have documented a mixotrophic algal wastewater treatment (A-WWT) system integrated with downstream technologies for recovering net energy and fertilizers from domestic wastewater. In the current study, we explore the potential for reclaiming reuse-quality water via the A-WWT system by treating its effluent further by granular activated carbon (GAC) adsorption or/and ozonation (O3). Our study also includes a comparison of water reclamation capability of a pilot-scale A-WWT system against that of a full-scale conventional activated sludge (CAS) system, both fed with the same primary effluent and followed by GAC and O3. In this preliminary evaluation, aggregate chemical water quality data collected from the following 8 treatment trains are compared: T1) CAS + GAC; T2) CAS + O3; T3) CAS + GAC + O3; T4) CAS + O3 + GAC; T5) A-WWT + GAC; T6) A-WWT + O3; T7) A-WWT + GAC + O3; and T8) A-WWT + O3 + GAC. Based on aggregate water quality measures, ozonation followed by GAC adsorption achieved the lowest concentrations of organics (dissolved organic carbon, chemical oxygen demand, and UV absorbance) and nutrients (total nitrogen and total phosphorus), irrespective of the treatment provided by the CAS and A-WWT systems. Despite the higher footprint requirement, all four algal-based treatment trains (T5 to T8) ranked better than the CAS-based trains (T1 to T4) when compared on the basis of energy demand and energy recoverability. Following these findings, a multi-criteria evaluation of the 8 treatment trains was performed considering 16 criteria spanning energy demand, energy recoverability, disinfection capability, emissions, areal footprint, and complexity. The multi-criteria evaluation ranked the A-WWT system integrated with ozonation and GAC adsorption (T8) highest among the eight treatment trains considered here. This preliminary evaluation adds further credence to the A-WWT system and warrants a detailed Water quality-based evaluation of its effluent and follow-up treatment to reclaim reuse-quality water.

Metagenomic profiling of antibiotic resistance and virulence removal: Activated sludge vs. algal wastewater treatment system

Conventional activated sludge-based (CAS) wastewater treatment plants are known to be a source of antibiotic resistance genes (ARGs) and virulence genes (VGs). As an alternative, a single-step mixotrophic algal wastewater treatment (A-WWT) system is proposed here to effectively reduce ARGs and VGs in the final effluent while meeting all the discharge standards. In this study, we applied the metagenomic profiling approach to compare the A-WWT system against the CAS system in terms of removal efficacy of ARG and VGs. A total of 111 ARG and 93 VG subtypes belonging to 10 antibiotic resistant classes and 19 virulence classes were detected in this study. Although the CAS system reduced the relative abundance of most classes of ARGs (7 of 10) and VGs (11 of 19), 3 ARG classes and 7 VG classes had increased abundances. On the other hand, the A-WWT system reduced the relative abundance of all classes of ARGs and VGs, and effectively eliminated most subtypes of ARGs and VGs. In the CAS system, the bacterial genera carrying ARGs and VGs was expanded, and the diversity index was increased greatly, suggesting the occurrence of horizontal gene transfer (HGT). In contrast, the A-WWT system narrowed down the potential host range and decreased their diversity substantially. Results of this study highlight the potential risk of ARGs and VGs in CAS system and demonstrate the feasibility of the algal-based system in removing ARGs and VGs.

Maximizing phosphorus recovery as biofertilizer in an algal wastewater treatment system

Our previous reports have demonstrated an algal pathway for treating settled sewage and recovering its energy-, nitrogen-, and phosphorous-contents via hydrothermal liquefaction (HTL) of the resulting algal biomass. The first part of the current study was to intensify a critical step in the phosphorous (P) recovery process which entails alkaline leaching of the P-rich byproduct of HTL– biochar, to yield a P-rich eluate. The following parameters driving the efficiency and cost of leaching P from biochar were systematically evaluated: leaching time, concentration of base eluent, mixing during leaching, liquid:solid (L:S) ratio in leaching, and temperature. Optimum leaching time, base concentration, L:S ratio, and temperature were found to be 72 h, 0.5 M, 20:1, and 60 °C, respectively. Under these optimal conditions, >86% of P in the biochar could be extracted at an estimated cost of $4.54/kg P. In the second part of this study, a three-step procedure was developed to recover high-purity biofertilizers from the P-rich eluate of biochar. In the first step, impurities along with 24.6% of P in the eluate were precipitated. In the second step, high-quality struvite (comprising 72.7% of P in the eluate) was precipitated from the supernatant of the first step. In the third step, the precipitate from the first step was dissolved and its P-content was re-precipitated as high-quality calcium phosphate. This three-step procedure resulted in 95.4% P-recovery from biochar eluate at $5.29/kg P. Reclaimed struvite and calcium phosphate were shown to be of high chemical purity, complying with US EPA guidelines for metals.

Carbon limitation in hypereutrophic, periphytic algal wastewater treatment systems.

Global eutrophication degrades water quality in freshwater ecosystems and limits the availability of freshwater for human consumption. While current wastewater treatment facilities (WWTF) remove pathogens and pollutants, many US WWTF continue to discharge nutrients that contribute to eutrophication. Traditional nutrient removal technologies can effectively reduce eutrophication risk, but can have unintended negative consequences on human and environmental health. Alternatives, such as algae-based treatment systems, improve the sustainability of the nutrient recovery process by producing biomass that can be converted to biofuel. However, research is needed to increase the productivity of algal treatment systems to improve their economic viability. Because algae in wastewater treatment systems are grown in wastewater rich in nutrients, the algae could become limited by dissolved inorganic carbon. This hypothesis was tested in 1.2 m long recirculating floways (n = 8 for each treatment/control) by quantifying algal dry mass and wastewater nutrient concentrations in 3 independent experiments: (1) carbon dioxide gas infused vs air infused control; (2) hydrochloric acid acidified vs neutralized solution control vs no chemical addition control; and (3) sodium bicarbonate addition vs no chemical control. Results showed increases in algal biomass after 18 days in wastewater augmented with dissolved inorganic carbon (carbon dioxide or sodium bicarbonate). In contrast, maintaining wastewater at near neutral pH with hydrochloric acid reduced algal productivity relative to controls. Nutrient reductions generally paralleled algal biomass increases except in the bicarbonate addition experiment. These findings provide evidence for the importance of carbon limitation in algal wastewater treatment floways. These results could help explain why carbon dioxide infusions stimulate algae in treatment systems. Furthermore, these results suggest that algae in nutrient enriched, sun-exposed streams (e.g., agricultural ditches or urbanized streams) may become carbon limited during peak periods of productivity. These findings could have important implications for ecosystems undergoing eutrophication as atmospheric carbon dioxide concentrations continue to rise.

Algal process for single-step removal of organic carbon and nutrients: Modeling and optimization of fed-batch operation

A process model to predict the performance of an emergent mixotrophic algal wastewater treatment system was developed and validated. Primary goal of this effort was to predict algal biomass production and the fed-batch cycle time, t*, required to meet the discharge standards under varying influent concentrations of organics and nutrients. Field data from the algal system fed with primary effluent at feed-to-culture volume ratio (Vf:Vc) of 400:300 were used to calibrate the model; additional data from runs with Vf:Vc = 400:300 and with Vf:Vc = 500:200 were used to validate the model. Predicted biomass production agreed well with the measured values in both cases, with r2 = 0.96–0.99, n = 40. Predicted t* also agreed well with the observed values in both cases, with r2 = 0.93–0.94, n = 30. Reasonable agreement was found between the predicted and measured day-to-day concentrations of biochemical oxygen demand (r2 = 0.97; n = 40), ammoniacal-nitrogen (r2 = 0.90; n = 120), and phosphate-phosphorus (r2 = 0.95; n = 120) with Vf:Vc = 400:300. Somewhat lower quality of predictions noted in the runs with Vf:Vc = 500:200 is attributed to the disproportional substrate removals resulting from the mismatch of stoichiometric C:N:P ratio between the algal species and the feed. Sensitivity analysis indicated the kinetic coefficient for phosphate-phosphorus reduction as the most sensitive parameter. Quality of the predictions in this study is comparable to that reported in the literature, but with fewer model parameters.

Recovery of struvite from hydrothermally processed algal biomass cultivated in urban wastewaters

A mixotrophic algal wastewater treatment system capable of reducing biochemical oxygen demand (BOD), ammoniacal nitrogen (NH4+-N), and phosphate (PO43−-P) in primary effluent in a single step has been demonstrated previously. Downstream processing of the resulting algal biomass by hydrothermal liquefaction (HTL) to recover its energy-content as biocrude oil has also been demonstrated. The current study evaluated the feasibility of recovering struvite from the two byproducts of HTL– a solid residue, rich in PO43–P; and an aqueous phase, rich in NH4+–N, for use as fertilizer. Results of this feasibility study and a preliminary mass balance model show that the proposed pathway can potentially yield ~2.5 kg struvite per 100 m3 of wastewater treated, recovering nearly 73% of PO43–P and 6% of NH4+–N in the primary effluent. Chemical and microscopic analysis of the wastewater-derived struvite revealed its composition to be close to that of pure struvite, with more than 12% P-content by weight. Scanning electron microscopy images depicted uniformly distributed sizes of irregular crystals in the wastewater-derived struvite. Low calcium content of this struvite indicated minimum amorphous calcium phosphate (ACP) impurities. Trace metal analysis showed that heavy metal levels in the recovered struvite were below current guidelines. This study confirmed the feasibility of recovering high-quality struvite from wastewaters, warranting further process optimization and characterization of the recovered struvite.

Metagenomic insights into virus removal performance of an algal-based wastewater treatment system utilizing Galdieria sulphuraria

An algal wastewater treatment system capable of reducing dissolved organics, nutrients, and pathogenic bacteria to secondary discharge standards in a single step has been reported on previously. The current study evaluates pathogenic virus reduction in this algal wastewater treatment system and compares it with that in conventional wastewater treatment systems using culture- and nucleic acid-based quantitative methods and shotgun metagenomic sequencing technique. Log removal of somatic coliphages (3.13 ± 0.34), F-specific coliphages (1.23 ± 0.34), Enterovirus (1.05 ± 0.32), and Norovirus GI (1.49 ± 0.16) in the algal wastewater treatment system without any chlorination were comparable to those in the conventional wastewater treatment system with chlorination. While the virus community in the chlorinated effluent of the conventional system was diverse with ~250 species, only 14 discrete virus species were found in the unchlorinated effluent of the algal-based system, none of them pathogenic to humans. This study demonstrated the feasibility of the A-WWT system in delivering pathogenically-safe, high-quality effluent for disposal or beneficial reuse with minimal post-disinfectant demand.

Predicting fecal coliform inactivation in a mixotrophic algal wastewater treatment system

Our previous reports have detailed the development of a pilot-scale algal wastewater treatment system (A-WWTS) utilizing a mixotrophic strain, Galdieria sulphuraria. This A-WWTS has consistently achieved discharge standards for organics and nutrients in a single step, concurrently reducing coliform bacteria to undetectable levels. Here, we present an approach to predict i) the fate of fecal coliform in this A-WWTS; and, ii) the fed-batch processing time required for a desired inactivation level. Specifically, a process model was developed to predict fecal coliform reduction under the synergistic effect of temperature, pH, and sunlight in terms of their individual first order inactivation rates. First-order temperature dependent inactivation rate at 20°C (k20) was established as 0.05h−1 with a temperature coefficient (θ) of 1.08. Inactivation coefficient due to the combined effects of sunlight was established as 0.647m2/MJ. The proposed approach was validated with experimental data from five scenarios; the quality of predictions of log removals spanning over five orders of magnitude (r2=0.947; n=12) was comparable to or better than those reported previously in inactivation studies. Utility value of this approach in forecasting fed-batch processing time under field conditions is illustrated.

Predicting removal kinetics of biochemical oxygen demand (BOD) and nutrients in a pilot scale fed-batch algal wastewater treatment system

Our previous reports have presented single-step treatment of primary-settled urban wastewater by a mixotrophic alga, Galdieria sulphuraria. Here, we present an approach to predict the operational cycle time, t*, required to meet the discharge standards for ammoniacal-nitrogen (NH3-N), phosphate (PO4) and biochemical oxygen demand (BOD) in fed-batch mode, under varying influent concentrations. First order removal rates of NH3-N, PO4 and BOD, determined using data from 10 fed-batch cycles in a pilot scale system (700 L), were used to predict their temporal fate and t* in 30 other cycles. Predicted concentrations of NH3-N, PO4, and BOD and t* over a wide range of influent concentrations agreed well with the measured ones, with root mean square errors, respectively, of 2.06 mg/L, 0.23 mg/L, 2.88 mg/L and 0.30 days. The coefficient of determination between the measured and the predicted values were as follows: for NH3-N: r2 = 0.82, n = 90; for PO4: r2 = 0.87, n = 90; for BOD: r2 = 0.70, n = 30; and for t*: r2 = 0.61, n = 30. The validity of the model in predicting temporal concentration profiles of NH3-N, PO4 and BOD reflected by Janus quotient (respectively of 0.85, 0.87 and 0.61) is comparable to or better than those reported in the literature. Sensitivity analysis procedures identified the influent concentration of PO4 as the most sensitive parameter in predicting t*.

Microalgae and sustainable wastewater treatment: a Review

Microalgae play important roles in the realisation of energy-efficient carbon-neutral wastewater treatment. This is achievable through coupling carbon capture with wastewater treatment and consequent biomass production. Unlike activated sludge, microalgal biomass is more of a resource than a waste. This paper presents a review on the use of microalgae in sustainable wastewater treatment including organic matter, nitrogen, phosphorus and heavy metals removal. The paper also focussed on microalgal cultivation systems and the potentials of using microalgal photosynthesis in satisfying bacterial oxygen requirements in hybrid algae-bacteria systems. The use of light-emitting diodes in microalgal photosynthesis and their prospects as promising light sources in hybrid algal wastewater treatment systems was also presented.Keywords: Bacteria; carbon capture; hybrid wastewater treatment systems; light-emittingdiodes; microalgae

Seasonal treatment and economic evaluation of an algal wastewater system for energy and nutrient recovery

Treatment efficacy and economic performance of an algal wastewater treatment and valorization system were evaluated in different seasons.

Factors contributing to bacteria inactivation in the Galdieria sulphuraria-based wastewater treatment system

Our previous pilot scale studies showed concurrent removals of biochemical oxygen demand and nutrients, and inactivation of pathogens in urban wastewaters by an extremophilic alga, Galdieria sulphuraria. The current work evaluated the following as potential factors contributing to the observed pathogen inactivation, using E. coli as a surrogate: bacterial toxicity of algal metabolites, culture pH and temperature, sunlight, dissolved oxygen and adsorption to algal biomass. Microtox toxicity results implied that algal metabolites were free of bacterial toxicants as the toxicity in the reactor decreased from 38.8% to zero in 4 days. Low cultivation pH of 4 was identified as the primary factor influencing E. coli reductions. At neutral pH, under sunlight, E. coli were reduced to undetectable levels in 24 h. But, in the presence of live algal biomass and sunlight, E. coli were reduced to undetectable levels within 12 h. We attribute this accelerated reduction of E. coli to the synergistic effect of sunlight and elevated dissolved oxygen levels generated by biomass in the reactor. Temperatures below 45 °C and adsorption of bacteria to algal biomass did not appear to cause inactivation of E. coli. Simulation of pilot-scale conditions confirmed that the synergistic effects of pH, sunlight, algal biomass, and dissolved oxygen contributed to the superior fecal coliform inactivation observed in the algal wastewater treatment system.

A NOVEL PROCESS OF WATER PURIFICATION SYSTEM FOR LARGE- SCALE PRODUCTIONS

Purification system has recently gained increasing importance, especially in water treatment systems. Biological water treatment systems with microalgae are now widely accepted. Moreover, algal wastewater treatment systems are effective when compared to conventional treatment systems. The proposed purification system aims to provide a process for using saline water, and saline reject water produced in water purification for gold mining production. Also, it provides a method for growing and harvesting algae utilizing saline water as growth medium for recycling waste water to extract the remaining metals from it. This trend of purification system using harvested algae has various applications, and may be used in wide aspects including, but not limited to, algae biomass production to extract metals, and reducing the cost of gold mining production.

Reduction of Organic and Inorganic Pollutant from Waste Water by Algae

Recently, algae have become significant organisms for biological purification of wastewater since they are able to accumulate plant nutrients, heavy metals, pesticides, organic and inorganic toxic substances and radioactive matters in their cells/bodies. Biological wastewater treatment systems with micro algae have particularly gained importance in last 50 years and it is now widely accepted that algal wastewater treatment systems are as effective as conventional treatment systems. These specific features have made algal wastewaters treatment systems an significant low-cost alternatives to complex expensive treatment systems particularly for purification of municipal wastewaters. By this method 70 % of biological oxygen demand, 66 % of chemical oxygen demand, 71 % total nitrogen, 67 % of phosphorus, 54 % volatile solid and 51 % of dissolved solid was reduced

Reduction of Organic and Inorganic Pollutant from Waste Water by Algae

Recently, algae have become significant organisms for biological purification of wastewater since they are able to accumulate plant nutrients, heavy metals, pesticides, organic and inorganic toxic substances and radioactive matters in their cells/bodies. Biological wastewater treatment systems with micro algae have particularly gained importance in last 50 years and it is now widely accepted that algal wastewater treatment systems are as effective as conventional treatment systems. These specific features have made algal wastewaters treatment systems an significant low-cost alternatives to complex expensive treatment systems particularly for purification of municipal wastewaters. By this method 70 % of biological oxygen demand, 66 % of chemical oxygen demand, 71 % total nitrogen, 67 % of phosphorus, 54 % volatile solid and 51 % of dissolved solid was reduced

Algal wastewater treatment systems for seasonal climates: Application of a simple modelling approach to generate local and regional design guidelines

Algal waste stabilisation ponds (WSP) provide a means of treating wastewater, and also a potential source of water for re-use in irrigation, aquaculture or algal biomass cultivation. The quantities of treated water available and the periods in which it is suitable for use or discharge are closely linked to climatic factors. This paper describes the application, at a continent-wide scale, of a modelling approach based on the use of readily available climate datasets to provide WSP design and performance guidelines linked to geographical location. Output is presented in regionally-based contour maps covering a wide area of Russia and central Asia and indicating pond area, earliest discharge date, discharge duration, wastewater inflow:outflow ratio and salinity under user-specified conditions. The results confirm that broad-brush discharge guidelines of the type commonly used in North America can safely be applied; but suggest that a more detailed approach is worthwhile to optimise operating regimes for local conditions. The use of long-series climate data can also permit tailoring of designs to specific sites. The work considers a simple 2-pond system, but other configurations and operating regimes should be investigated, especially for the wide range of locations across the world that are intermediate between the ‘one short discharge per year’ mode and year-round steady-state operation.

PH Buffer Capacity Based Monitoring of Algal Wastewater Treatment

A pH buffer capacity based method for multivariate monitoring of tertiary algal wastewater treatment systems is presented. A pilot plant with algal biomass receiving the effluent of a carbon removing activated sludge municipal wastewater treatment plant was used for the experimental work. Two types of buffer capacity profiles are considered, first resulting from a titration from the actual pH to pH 2.5 (down titration), and second as a result of a titration from pH 2.5 to pH 11 (up titration). The experiments were conducted with a laboratory titrator and the buffer capacity profiles were processed by fitting mathematical models of buffer systems to them. This allowed quantification of the inorganic carbon (IC) buffer from the down titration profiles. IC is of major importance because it is the only carbon source used by algae. It is shown that the IC concentration derived from the buffer capacity profile gives different process information than a standard alkalinity measurement. The up titration profiles were successfully used for the quantification of NH4 − and o-PO4, although an exact comparison of the laboratory results and the buffer capacity based results is difficult, because of the filtration step preceding laboratory analyses and possible interferences caused by unmodeled buffer systems. No filter device was used, which makes it possible to implement this measurement method in a robust and field applicable sensor. The complete measurement cycle (down titration followed by up titration and data interpretation) can be performed in less than 1 hour, with little manipulation, and could easily be automated.

Tube settling of high-rate pond algae

The effluent of a high-rate pond (HRP) may contain 200 to 400 mg/L of algal suspended solids (SS). Microalgae must be separated before the effluent is discharged. Gravity sedimentation is usually the first method considered in algal wastewater treatment systems. However, required overflow rates (OFRs) to remove algae in the conventional clarifiers are too low. Therefore, the shallow-depth sedimentation concept was studied for the separation of Micractinium from HRP effluent in order to increase the OFRs of gravity settling equipment. Using the orthogonal squares experimental plan, the design parameters, such as OFR, tube diameter, tube length, and inclination, were evaluated for algal SS removal. A circular upflow clarifier was run as a control. At an OFR of 8.15 L/m2 · min (0.2 gpm/ft2), SS removal efficiencies of tube settling and upflow clarifier were 80% and 18%, respectively. When the OFR was increased to 16.3 L/m2 · min (0.4 gpm/ft2), SS removal efficiencies decreased to 61% in tube settler and to 11% in upflow clarifier. SS removal efficiencies of tube settlers were 40% at 30.6 L/m2 · min (0.75 gpm/ft2) and 20% at 71.3 L/m2 · min (1.75 gpm/ft2). A linear relationship exists between removal efficiency and the diameter and length of tubes. The relationship is parabolic for the inclination of tubes and the OFR. The overall algae removal efficiency increased with the tube length but it was an inverse function of OFR, tube diameter, and inclination. At an OFR of 12.2 L/m2 · min (0.3 gpm/ft2), algae removal efficiencies were 7 to 8 times better than that of upflow clarifier. It was demonstrated that OFR in a gravity settler could be increased 4 to 5 times using tube settlers.

Tube settling of high-rate pond algae

The effluent of a high-rate pond (HRP) may contain 200 to 400 mg/L of algal suspended solids (SS). Microalgae must be separated before the effluent is discharged. Gravity sedimentation is usually the first method considered in algal wastewater treatment systems. However, required overflow rates (OFRs) to remove algae in the conventional clarifiers are too low. Therefore, the shallow-depth sedimentation concept was studied for the separation of Micractinium from HRP effluent in order to increase the OFRs of gravity settling equipment. Using the orthogonal squares experimental plan, the design parameters, such as OFR, tube diameter, tube length, and inclination, were evaluated for algal SS removal. A circular upflow clarifier was run as a control. At an OFR of 8.15 L/m2 . min (0.2 gpm/ft2), SS removal efficiencies of tube settling and upflow clarifier were 80% and 18%, respectively. When the OFR was increased to 16.3 L/m2 · min (0.4 gpm/ft2), SS removal efficiencies decreased to 61% in tube settler and to I 1% in upflow clarifier. SS removal efficiencies of tube settlers were 40% at 30.6 L/m2 . min (0.7S gpm/ft2) and 20% at 71.3 L/m2 · min (1.7S gpm/ft2). A linear relationship exists between removal efficiency and the diameter and length of tubes. The relationship is parabolic for the inclination of tubes and the OFR. The overall algae removal efficiency increased with the tube length but it was an inverse function of OFR, tube diameter, and inclination. At an OFR of 12.2 L/m2 · min (0.3 gptn/ft2), algae removal efficiencies were 7 to 8 times better than that of upflow clarifier. It was demonstrated that OFR in a gravity settler could be increased 4 to 5 times using tube settlers.