High Rate Algal Ponds Research Articles

Fatty acids from high rate algal pond’s microalgal biomass and osmotic stress effects

The extraction of oil from a wild microalgae biomass collected from a domestic wastewater treatment facility’s high rate algal pond (HRAP) was investigated. An experiment plan was used to determine the most efficient extraction method, the optimal temperature, time and solvent system based on total lipids yield. Microwave-assisted extraction was the most efficient method whether in n-hexane or in a mixture of chloroform/methanol compared to Soxhlet, homogenization, and ultrasounds assisted extractions. This same wild biomass was cultivated in a photobioreactor (PBR) and the effect of osmotic stress was studied. The lipids extraction yield after 3days of stress increased by more than four folds without any significant loss of biomass, however, the quality of extracted total lipids in terms of saturated, monounsaturated and polyunsaturated fatty acids was not affected by salinity change in the culture medium.

Environmental drivers that influence microalgal species in fullscale wastewater treatment high rate algal ponds

In the last decade, studies have focused on identifying the most suitable microalgal species for coupled high rate algal pond (HRAP) wastewater treatment and resource recovery. However, one of the challenges facing outdoor HRAP systems is maintaining microalgal species dominance. By increasing our understanding of the environmental drivers of microalgal community composition within the HRAP environment, it may be possible to manipulate the system in such a way to favour the growth of desirable species. In this paper, we investigate the microalgal community composition in two full-scale HRAPs over a 23-month period. We compare wastewater treatment performance between dominant species and identify the environmental drivers that trigger change in community composition. A total of 33 microalgal species were identified over the 23-month period but species richness (the number of species present at any given time) was low and was not related to either productivity or nutrient removal efficiency. Species turnover of the dominant microalgae happened rapidly, typically <1 week. Changes in the influent NH4-N concentration and zooplankton grazer numbers were significantly associated with species turnover, accounting for 80% of the changes in dominant species throughout the 23-month study period. Both nutrient removal and biomass production did not differ between the two HRAPs when the dominant species was the same or differed in the two ponds. These results suggest that microalgal functional groups are more important than individual species for full-scale HRAP performance. This study has increased our understanding of some of the environmental drivers of the microalgae within the HRAP environment, which may assist with improving wastewater treatment and resource recovery.

Control of zooplankton populations in a wastewater treatment High Rate Algal Pond using overnight CO2 asphyxiation

High Rate Algal Ponds (HRAPs) with addition of CO2 are open pond wastewater treatment systems that recover nutrients as microalgal biomass. Such ponds are vulnerable to contamination by opportunistic zooplankton species able to survive the wastewater HRAP environment. The high food availability and a near neutral pH can promote the rapid development of high densities of zooplankton that can reduce treatment performance by consuming microalgae. Zooplankton control using night time CO2 asphyxiation was selected from promising zooplankton control methods previously screened at laboratory and mesocosm scales, and used to control zooplankton densities in an 8m3 HRAP over 14months. Increasingly higher flow rates (1 to 6L/min) of pure CO2 were tested by using 13 control treatment events. CO2 was injected during night time, and treatment events were repeated for a number of consecutive nights sufficient to control zooplankton density to ≤10% of that before treatment. Treatments with higher CO2 flow rates promoted more rapid reductions of zooplankton density (12 nights to 1), and were associated with higher maximum CO2 concentrations (100 to 420mg/L), and lower pH (~6 to ~5). Compared to the control HRAP, CO2 treatment decreased the average population densities of some zooplankton species over the experimental period: Moina tenuicornis (41.3%), Paracyclops fimbriatus (43.9%), Filinia longiseta (59.8%), but was associated with higher average population densities of others: Heterocypris incongruens (174.4%), Asplanchna sieboldi (177.8%), Cephalodella catellina (200.0%), and Brachionus calyciflorus (234.9%). However, the population densities of the rotifers B. calyciflorus and C. catellina were always reduced following CO2 treatments with flow rates ≥2L/min. The cladoceran Daphnia thomsoni and the rotifer Brachionus urceolaris established only in the control HRAP. Zooplankton control by CO2 asphyxiation improved the overall performance of the treated WW HRAP compared to the control in several ways, including increasing algal biomass (VSS) (150.8%), productivity (151.4%), chlorophyll-a concentration (161.8%), particle size (MCSA) (115.8%), and average settleability efficiency (189.2%). Overnight CO2 asphyxiation showed the potential to control zooplankton and to promote better WW HRAPs performance.

Extracellular polymeric substance production in high rate algal oxidation ponds

Integrated algal pond systems (IAPSs) combine anaerobic and aerobic bioprocesses to affect sewage treatment. The present work describes the isolation and partial characterisation of soluble extracellular polymeric substances (EPSs) associated with microalgal bacterial flocs (MaB-flocs) generated in high rate algal oxidation ponds (HRAOPs) of an IAPS treating domestic sewage. Productivity and change in MaB-flocs concentration, measured as mixed liquor suspended solids (MLSS) between morning (MLSSAM) and evening (MLSSPM) were monitored and the substructure of the MaB-flocs matrix examined by biochemical analysis and Fourier transform infrared spectroscopy (FT-IR). Results show that MaB-flocs from HRAOPs are assemblages of microorganisms produced as discrete aggregates as a result of microbial EPS production. Formation and accumulation of the EPS was stimulated by light. Analysis by FT-IR revealed characteristic carbohydrate enrichment of these polymeric substances. In contrast, FT-IR spectra of EPSs from dark-incubated MaB-flocs confirmed that these polymers contained increased aliphatic and aromatic functionalities relative to carbohydrates. These differences, it was concluded, were due to dark-induced transition from phototrophic to heterotrophic metabolism. The results negate microalgal cell death as a contributor to elevated chemical oxygen demand of IAPS treated water.

Short term effects of treated greywater by high rate algal ponds process on vegetable yield and soil properties under Sudano‐Sahelian climate conditions

Greywater is a valuable additional water source for agriculture in arid and semi‐arid countries subject to water scarcity. However, the impacts of applying greywater to agricultural land in the Sudano‐Sahelian regions are not adequately understood. This study evaluates the impacts of using greywater, treated by the High Rate Algal Ponds system (HRAPs), on soil characteristics and okra growth and yield in the Sudano‐Sahelian regions. The methodology consisted of growing okra under four different irrigation conditions: (i) treated greywater (TGW); (ii) fresh well water (FWW); (iii) TGW and chemical fertilizer (TGW + FERT) and (iv) FWW and chemical fertilizer (FWW + FERT). The test beds were sampled before and after cultivation to analyze soil pH and sodicity status (e.g., sodium absorption ratio: SAR). The okra growth, fruit yield and total dry biomass were recorded. Fresh fruit weight is significantly higher with TGW (761.17 ± 53.69 kg.ha−1) compared to FWW (497.15 ± 100.02 kg.ha−1) and FWW + FERT (307.93 ± 100.04 kg.ha−1). This result likely occurs due to the nutrients (e.g., nitrogen) present in TGW. Conversely, the average SAR of soil irrigated with TGW + FERT (12.47) and TGW (8.83) are significantly higher than those of the soil irrigated with FWW (2.92) and soil before cultivation (0.95). Therefore, it is recommended that soil salinity or/and sodicity is monitored when irrigating with TGW and that well water is used for every third irrigation cycle to prevent soil degradation though increased salinity. Overall, the appropriate reuse of greywater improves food security and the sustainability of agriculture in arid to semi‐arid regions. © 2017 American Institute of Chemical Engineers Environ Prog, 37: 465–470, 2018

Biomass granulation in an upflow anaerobic sludge blanket reactor treating 500 m3/day low-strength sewage and post treatment in high-rate algal pond.

A pilot-scale upflow anaerobic sludge blanket-moving bed biofilm (UASB-MBB) reactor followed by a high-rate algal pond (HRAP) was designed and operated to remove organic matter, nutrients and pathogens from sewage and to facilitate reuse. For an influent chemical oxygen demand (COD) concentration of 233 ± 20 mg/L, final effluent COD was 50 ± 6 mg/L. Successful biomass granulation was observed in the sludge bed of the upflow anaerobic sludge blanket (UASB) reactor after 5 months of operation. Ammonia removal in HRAP was 85.1 ± 2.4% with average influent and effluent ammonia nitrogen concentrations of 20 ± 3 mg/L and 3 ± 1 mg/L, respectively. Phosphate removal after treatment in the HRAP was 91 ± 1%. There was a 2-3 log scale pathogen removal after treatment in HRAP with most probable number (MPN) of the final effluent being 600-800 per 100 mL, which is within acceptable standards for surface irrigation. The blackwater after treatment in UASB-MBBR-HRAP is being reused for gardening and landscaping. This proper hydro-dynamically designed UASB reactor demonstrated successful granulation and moving bed media improved sludge retention in UASB reactor. This combination of UASB-MBB reactor followed by HRAP demonstrated successful sewage treatment for a year covering all seasons.

Life Cycle Assessment of wastewater treatment systems for small communities: Activated sludge, constructed wetlands and high rate algal ponds

The aim of this study was to assess the environmental impact of three alternatives for wastewater treatment in small communities. To this end, a Life Cycle Assessment (LCA) was carried out comparing a conventional wastewater treatment plant (i.e. activated sludge system) with two nature-based technologies (i.e. hybrid constructed wetland and high rate algal pond systems). Moreover, an economic evaluation was also addressed. All systems served a population equivalent of 1500 p.e. The functional unit was 1 m3 of water. System boundaries comprised input and output flows of material and energy resources for system construction and operation. The LCA was performed with the software SimaPro®8, using the ReCiPe midpoint method. The results showed that the nature-based solutions were the most environmentally friendly alternatives, while the conventional wastewater treatment plant presented the worst results due to the high electricity and chemicals consumption. Specifically, the potential environmental impact of the conventional wastewater treatment plant was between 2 and 5 times higher than that generated by the nature-based systems depending on the impact category. Even though constructed wetland and high rate algal pond systems presented similar results in terms of environmental impact, the latter showed to be the less expensive alternative. Nevertheless, the constructed wetland system should be preferred when land occupation is of major concern, since it has a smaller footprint compared to the high rate algal pond alternative.

Microalgal diversity fosters stable biomass productivity in open ponds treating wastewater

It is established that biodiversity determines productivity of natural ecosystems globally. We have proved that abiotic factors influenced biomass productivity in engineered ecosystems i.e. high rate algal ponds (HRAPs), previously. This study demonstrates that biotic factors, particularly microalgal diversity, play an essential role in maintaining stable biomass productivity in HRAP treating municipal wastewater by mutualistic adaptation to environmental factors. The current study examined data from the second year of a two-year study on HRAP treating municipal wastewater. Microalgal diversity, wastewater characteristics, treatment efficiency and several environmental and meteorological factors were documented. Multivariate statistical analyses reveal that microalgae in uncontrolled HRAPs adapt to adverse environmental conditions by fostering diversity. Subsequently, five dominant microalgal strains by biovolume were isolated, enriched, and optimum conditions for high biomass productivity were ascertained. These laboratory experiments revealed that different microalgal strains dominate in different conditions and a consortium of these diverse taxa help in sustaining the algae community from environmental and predatory pressures. Diversity, niche or seasonal partitioning and mutualistic growth are pertinent in microalgal cultivation or wastewater treatment. Therefore, enrichment of selective species would deprive the collective adaptive ability of the consortium and encourage system vulnerability especially in wastewater treatment.

Mini-review: high rate algal ponds, flexible systems for sustainable wastewater treatment.

Over the last 20years, there has been a growing requirement by governments around the world for organisations to adopt more sustainable practices. Wastewater treatment is no exception, with many currently used systems requiring large capital investment, land area and power consumption. High rate algal ponds offer a sustainable, efficient and lower cost option to the systems currently in use. They are shallow, mixed lagoon based systems, which aim to maximise wastewater treatment by creating optimal conditions for algal growth and oxygen production-the key processes which remove nitrogen and organic waste in HRAP systems. This design means they can treat wastewater to an acceptable quality within a fifth of time of other lagoon systems while using 50% less surface area. This smaller land requirement decreases both the construction costs and evaporative water losses, making larger volumes of treated water available for beneficial reuse. They are ideal for rural, peri-urban and remote communities as they require minimum power and little on-site management. This review will address the history of and current trends in high rate algal pond development and application; a comparison of their performance with other systems when treating various wastewaters; and discuss their potential for production of added-value products. Finally, the review will consider areas requiring further research.

Ciprofloxacin removal during secondary domestic wastewater treatment in high rate algal ponds

This study investigated the removal of antibiotic ciprofloxacin during the treatment of real wastewater using high rate algal ponds (HRAP). When spiked at 2 mg/L into primary domestic wastewater, ciprofloxacin (CPX) was efficiently removed from laboratory scale photobioreactors continuously operated under various durations of artificial illumination and hydraulic residence times. Subsequent batch tests conducted with reactor microcosms showed CPX removal was mainly caused by photodegradation during daytime, and sorption to biomass during night time. These findings were confirmed during an experiment conducted in a 1000 L pilot HRAP operated outdoors, as well as during outdoor batch assays conducted using pilot HRAP microcosms. While these results highlight a potentially interesting treatment capacity in comparison to conventional biological treatment, further research must confirm these findings at relevant pollutant concentration (ng-μg/L) and determine the fate and potential toxicity of degradation products.

Understanding the biological activity of high rate algae ponds through the calculation of oxygen balances.

Microalgae culture in high rate algae ponds (HRAP) is an environmentally friendly technology for wastewater treatment. However, for the implementation of these systems, a better understanding of the oxygenation potential and the influence of climate conditions is required. In this work, the rates of oxygen production, consumption, and exchange with the atmosphere were calculated under varying conditions of solar irradiance and dilution rate during six months of operation in a real scale unit. This analysis allowed determining the biological response of these dynamic systems. The rates of oxygen consumption measured were considerably higher than the values calculated based on the organic loading rate. The response to light intensity in terms of oxygen production in the bioreactor was described with one of the models proposed for microalgae culture in dense concentrations. This model is based on the availability of light inside the culture and the specific response of microalgae to this parameter. The specific response to solar radiation intensity showed a reasonable stability in spite of the fluctuations due to meteorological conditions. The methodology developed is a useful tool for optimization and prediction of the performance of these systems.

Assessment of potential zooplankton control treatments for wastewater treatment High Rate Algal Ponds

Cladocerans and rotifers rapidly consume beneficial microalgae and reduce the performance of High Rate Algal Ponds (HRAPs) for wastewater treatment and algal production. Potential zooplankton control treatments for HRAPs have been proposed and tested at a laboratory scale including CO2 asphyxiation, biological control using competitor species, filtration, and mechanical disruption using hydrodynamic shear stress. This paper aims to validate these treatments using outdoor mesocosms with physicochemical and operational conditions similar to those of full scale HRAPs. A continuous CO2 concentration of ~100mg/L maintained low pond water zooplankton densities, while a continuous concentration of ~180mg/L killed all microcrustaceans and rotifers present. As biocontrol agents, the cladoceran Moina tenuicornis at ~2000 individuals/L reduced average rotifer densities by 90% while the ostracod Heterocypris incongruens at ~1000 individuals/L removed all rotifers. Mechanical filtration using 300μm and 500μm filters eradicated M. tenuicornis after one and four filtration periods, respectively. Mechanical hydrodynamic stress killed up to 100% of microcrustaceans, and ~50% of larger rotifers. Furthermore, phototaxis-induced migration promoted higher densities of M. tenuicornis in the upper layer of the water column in an 8m3 HRAP during periods of low solar radiation, suggesting that mechanical treatments should be performed at night and to the upper layer of the pond water. Overall, CO2 asphyxiation appeared to be the most reliable, versatile, and effective zooplankton control treatment.

A study of photosynthetic biogas upgrading based on a high rate algal pond under alkaline conditions: Influence of the illumination regime

Microalgal-bacterial processes have emerged as environmental friendly systems for the cost-effective treatment of anaerobic effluents such as biogas and nutrients-laden digestates. Environmental parameters such as temperature, irradiation, nutrient concentration and pH effect the performance of the systems. In this paper, the potential of a microalgal-bacterial photobioreactor operated under high pH (≈9.5) and high alkalinity to convert biogas into biomethane was evaluated. The influence of the illumination regime (continuous light supply vs 12h/12h light/dark cycles) on the synthetic biogas upgrading efficiency, biomass productivity and nutrient removal efficiency was assessed in a High-Rate Algal Pond interconnected to a biogas absorption bubble column. No significant differences in the removal efficiency of CO2 and H2S (91.5±2% and 99.5%±0.5, respectively) were recorded regardless of the illumination regime. The high fluctuations of the dissolved oxygen concentration during operation under light/dark cycles allowed to evaluate the specific growth rate and the specific partial degradation rate of the microalgae biomass by photosynthesis and respiration, respectively. The respiration reduced the net microalgae biomass productivity under light/dark cycles compared with process operation under the continuous light supply.

Optimization of pilot high rate algal ponds for simultaneous nutrient removal and lipids production

Special attention is required to the removal of nitrogen and phosphorous in treated wastewaters. Although, there are a wide range of techniques commercially available for nutrient up-take, these processes entail high investment and operational costs. In the other hand, microalgae growth can simultaneously remove inorganic constituents of wastewater and produce energy rich biomass. Among all the cultivation technologies, High Rate Algae Ponds (HRAPs), are accepted as the most appropriate system. However, the optimization of the operation that maximizes the productivity, nutrient removal and lipid content in the biomass generated has not been established. In this study, the effect of two levels of depth and the addition of CO2 were evaluated. Batch essays were used for the calculation of the kinetic parameters of microbial growth that determine the optimum conditions for continuous operation. Nutrient removal and lipid content of the biomass generated were analyzed. The best conditions were found at depth of 0.3m with CO2 addition (biomass productivity of 26.2gTSSm−2d−1 and a lipid productivity of 6.0glipidsm−2d−1) in continuous mode. The concentration of nutrients was in all cases below discharge limits established by the most restrictive regulation for wastewater discharge.

Simultaneous biogas upgrading and centrate treatment in an outdoors pilot scale high rate algal pond

The bioconversion of biogas to biomethane coupled to centrate treatment was evaluated in an outdoors pilot scale high rate algal pond interconnected to an external CO2-H2S absorption column (AC) via settled broth recirculation. CO2-removal efficiencies ranged from 50 to 95% depending on the alkalinity of the cultivation broth and environmental conditions, while a complete H2S removal was achieved regardless of the operational conditions. A maximum CH4 concentration of 94% with a limited O2 and N2 stripping was recorded in the upgraded biogas at recycling liquid/biogas ratios in the AC of 1 and 2. Process operation at a constant biomass productivity of 15gm−2d−1 and the minimization of effluent generation supported high carbon and nutrient recoveries in the harvested biomass (C=66±8%, N=54±18%, P≈100% and S=16±3%). Finally, a low diversity in the structure of the microalgae population was promoted by the environmental and operational conditions imposed.

Photodegradation and sorption govern tetracycline removal during wastewater treatment in algal ponds

The degradation of the antibiotic tetracycline, supplied at 100µgL−1 in domestic wastewater, was studied in an outdoor, pilot scale, high rate algal pond (HRAP). Effective operation was demonstrated with the biomass concentration and the chemical oxygen demand removal efficiency averaging 1.2±0.1gTSSL−1 and 80±4%, respectively, across all operational periods. Tetracycline removal exceeded 93% and 99% when the HRAP was operated at hydraulic retention times of 4 and 7days, respectively. Batch tests and pulse testing during HRAP operation repeatedly evidenced the significance of photodegradation as a removal mechanism. Sorption dominated tetracycline removal during the night, but accounted for less than 6% of the total pollutant removal based on sorbed tetracycline extracted from biomass. Overall, these results provide the first demonstration of efficient antibiotic removal, occurring mainly via indirect photodegradation, during relevant HRAP operation (low pollutant concentration, domestic wastewater and natural sunlight).

Thermal pretreatment and bioaugmentation improve methane yield of microalgal mix produced in thermophilic anaerobic digestate

Liquid fraction produced in anaerobic digestion (AD) of biodegradable waste can be treated on-site with microalgae, which can be recycled back as substrate to the biogas plant. For this research, a pilot high rate algal pond (HRAP) was set with connections to a full scale biogas plant that enabled the use of waste heat and CO2 from a combined heat and power gen-set (CHP). The microalgal mix produced in the thermophilic anaerobic digestate supernatant was tested as a substrate for biogas production in the thermophilic AD (i.e. untreated, bioaugmented with anaerobic bacteria Clostridium thermocellum, and thermally pretreated, respectively). The methane potential of the untreated microalgal mix was low (157.5 ± 18.7 mL CH4/g VS). However, after the thermal pretreatment of the microalgae, methane production increased by 62%, while in the bioaugmentation with C. thermocellum under thermophilic conditions (T = 55 °C) it was elevated by 12%. The outcome of our pilot trial suggests that microalgae produced in the thermophilic biogas digestate represent a prospective alternative AD feedstock. At the same time, microalgae reduce the digestate nitrogen and COD to the level sufficient for the outflow to meet the quality required by the sewage system (ammonia-nitrogen max 200 mg/L, nitrite max 10 mg/L).

Microbial community structures in high rate algae ponds for bioconversion of agricultural wastes from livestock industry for feed production.

Dynamics of seasonal microbial community compositions in algae cultivation ponds are complex. However, there is very limited knowledge on bacterial communities that may play significant roles with algae in the bioconversion of manure nutrients to animal feed. In this study, water samples were collected during winter, spring, summer, and fall from the dairy lagoon effluent (DLE), high rate algae ponds (HRAP) that were fed with diluted DLE, and municipal waste water treatment plant (WWTP) effluent which was included as a comparison system for the analysis of total bacteria, Cyanobacteria, and microalgae communities using MiSeq Illumina sequencing targeting the 16S V4 rDNA region. The main objective was to examine dynamics in microbial community composition in the HRAP used for the production of algal biomass. DNA was extracted from the different sample types using three commercially available DNA extraction kits; MoBio Power water extraction kit, Zymo fungi/bacterial extraction kit, and MP Biomedicals FastDNA SPIN Kit. Permutational analysis of variance (PERMANOVA) using distance matrices on each variable showed significant differences (P=0.001) in beta-diversity based on sample source. Environmental variables such as hydraulic retention time (HRT; P<0.031), total N (P<0.002), total inorganic N (P<0.002), total P (P<0.002), alkalinity (P<0.002), pH (P<0.022), total suspended solid (TSS; P<0.003), and volatile suspended solids (VSS; P<0.002) significantly affected microbial communities in DLE, HRAP, and WWTP. Of the operational taxonomic units (OTUs) identified to phyla level, the dominant classes of bacteria identified were: Cyanobacteria, Alpha-, Beta-, Gamma-, Epsilon-, and Delta-proteobacteria, Bacteroidetes, Firmicutes, and Planctomycetes. Our data suggest that microbial communities were significantly affected in HRAP by different environmental variables, and care must be taken in extraction procedures when evaluating specific groups of microbial communities for specific functions.

レースウェイ型微細藻類培養槽（HRAP）の大型動物プランクトン除去による 汚水処理性能および微細藻類への影響

レースウェイ型微細藻類培養槽（HRAP）の大型動物プランクトン除去による 汚水処理性能および微細藻類への影響

Integrating nutrient removal and solid management restricts the feasibility of algal biofuel generation via wastewater treatment

While numerous studies have demonstrated the efficiency of secondary wastewater treatment (WWT) in high rate algae ponds (HRAPs), little consideration has been given to how the algal unit should be best integrated within a full treatment system complying with typical nutrient discharge standards. Using the case study of a 2000 person equivalent (P.E.), we first demonstrate that algal treatment is most efficiently used for combined carbon and nutrient removal because an HRAP designed for compliant N (or P) removal de facto provides free and environmentally-benign carbon removal. The large O2 excess capacity for aerobic carbon removal also suggests primary suspended solid removal is unlikely needed, although grit removal remains necessary. We then demonstrate combining algal cultivation with anaerobic digestion is not economic at small scale because it offers marginal energy savings (e.g. 10.7€P.E.−1yr−1) while incurring significant costs for digestate transport offsite (e.g. 32.5€P.E.−1y−1 at a distance of 50km). Subsequent sensitivity analyses confirmed that while the potential of algae-to-biogas via WWT is limited (e.g. total cost of 38.2€P.E.−1y−1 in our base case), integrating the use of HRAPs with solar drying has the potential to provide a more economical and energy-efficient WWT alternative for nutrient removal and recovery (24.4€P.E.−1y−1).