Algal Ponds Research Articles

Medicinal impact of microalgae collected from high rate algal ponds; phytochemical and pharmacological studies of microalgae and its application in medicated bandages

Abstract In the course of maximizing the utilization of natural resources, microalgal communities growing in high rate algal ponds are being investigated for possible pharmacological and medicinal values. An algal community predominated by Microcystis aeruginosa was phytochemically studied using Liquid chromatography with Photodiode array detector coupled with electron spary ionization mass spectroscopy (LC-DAD/ESI-MS). A pharmacological screening including antioxidant, anti-inflammatory, anti-diabetic and cytotoxic actions was conducted. The application of Microcystis aeruginosa predominant algal extract in formulating medicated bandages to aid healing of diabetic wounds was further evaluated. The phytochemical investigation of the algal extract led to the separation and identification of hydroxypheophytin-a, astaxanthin and phytoene in the algal extract which showed marked antioxidant and anti-inflammatory activities at 500 mg/kg dose level. At a dose of 200 and 400 mg/kg, it significantly diminished glucose levels in diabetic rats' sera in a dose-dependent manner. Marked decline in serum nitric oxide and catalase values was detected along with a significant increase in serum insulin, glucose transporter 2 and cluster of differentiation 4 levels. The obtained results indicated that the use of the algal based medicated bandages on wounds induced in diabetic rats showed progressive healing as compared to untreated rats. A considerable decrease in serum tumor necrosis factor-α accompanied by the increase in serum collagen-I was observed. The histopathological inspection of rats’ skin ascertained the improvement in skin condition.

Potential Use of High Rate Algae Ponds for Resource Recovery in the Water-Food-Energy Nexus for Tanzania: A Review

The use of High Rate Algal Ponds (HRAPs) for the treatment of wastewater and resource recovery has raised interest in recent years. Treatment of wastewater through this technology has proved to have high efficiency in reducing the level of pollution, nutrients, dissolved solids as well as pathogens. HRAPs are more efficient than conventional Wastewater Stabilization Ponds (WSPs) due to their design approach that provides room for high rate bio-chemical processes, which increase the mechanisms of nutrients and pathogens removal as well as the rate of micro-algae production for purposes of resource recovery. This paper reviews the upgrading potential of existing WSPs to HRAPs for resource recovery from products of wastewater for biofuel production, as a plant nutrient or for irrigation purposes and animal feeding. Several results have reported HRAPs to have efficiency in reducing bacterial contamination in excess of 99% while the removal of organic matter of up to 84% for Chemical Oxygen Demand (COD) and 88% for Biochemical Oxygen Demand under normal conditions have been reported. The removal for nitrogen was indicated to vary from 50 t0 98% while that of phosphorus varies from 32 to 99% depending on the culture conditions. It was further noted that, the potential for resource recovery from HRAPs is high in terms of energy and nutrients recovered through algae biomass, particularly for biofuel and animal feed production. Whereas among the dominant algal species of the HRAP Chlorella vulgaris revealed to have suitability in both treatment of wastewater and achieved a higher effluent quality and having nutrients contents essential for lipid extraction for biofuel and as a protein source for animal feeding which is largely attributed by their ability to grow very rapidly and to tolerate varieties of cultural conditions. To date, limited research attention has been given to studying the re-use potential of wastewater for irrigation purposes in Africa.

Model exploration of interactions between algal functional diversity and productivity in chemostats to represent open ponds systems across climate gradients

Eukaryotic microalgae and prokaryotic cyanobacteria (often collectively described as algae) have been proposed as a promising commercially viable feedstock for biofuels and other bioproducts. Open pond algal monocultures are subjected to environmental fluctuations (i.e. temperature), limiting productivity as environmental conditions vary. An approach to overcome such limitation is the replacement of monocultures with customized polycultures that leverage diversity-productivity relationships by exploiting complementary but uninhabited ecological niches. Defining ecological niche complementarity requires an understanding of how traits and trade-offs interact across environmental gradients and for this reason numerical models represent valuable tools to explore the possible solution space prior to experimental design and verification. We have developed a trait-based, dynamic energy budget model (TB-DEB) of microalgal monocultures and polycultures, and simulated the growth of random and customized polycultures under environmental conditions (i.e. temperature, photoperiod) similar to those in operational algal ponds across the US. Each of the algal species selected as a polyculture component is defined by distinct combinations of literature-derived traits related to substrate uptake, light utilization and temperature optima. Members of the polycultures were categorized into algal functional guilds that were defined based on the interaction between thermal traits and pond thermal regimes. When compared to guilds defined by taxonomy, we demonstrate that grouping algal guilds by functional traits can be an effective approach towards improving biomass productivity in operational algal ponds. Simulations show that a polyculture represents the equivalent of a wider niche monoculture, leading to sustained productivity across seasons. Simulations also revealed that higher species diversity and higher functional diversity lead to higher system biomass. In all, results from this modeling study and earlier experimental studies highlight the idea that regardless of the functional group definition, systematic selection of species based on knowledge of physiology, ecology and the environment aiming at maximizing use of niche space through complementarity has positive impacts on system productivity.

Analysis of polyhydroxybutrate and bioplastic production from microalgae

BackgroundAlgae manufacture a diversity of base materials that can be used for bioplastics assembly. The most essential compounds are carbohydrates and hydrocarbons. Polyhydroxybutyrate (PHB) is a polymer belonging to the polyester class that is of interest as bio-derived and biodegradable plastics.ResultsIn this study, three microalgal strains in addition to two microalgal biomass collected from high-rate algal ponds (HRAP) were used to detect their ability to produce polyhydroxybutrate for bioplastic production. The results showed that among the selected strains, Microcystis aeruginosa has the highest polyhydroxybutrate concentration (0.49 ± 0.5 mg mL−1). However, the biomass collected from the high-rate algal pond dominated with Microcystis sp. showed a higher concentration (0.7 ± 0.6 mg mL−1).ConclusionThe biomass collected from the high-rate algal pond dominated with Microcystis sp. was used for producing bioplastic since it has the highest concentration of PHB. Referring to plasticizing capacity, elongation at break (%) for algal biomass was 530% which was higher than that detected in blank which was 307%. So, it was obvious that the algal bioplastic has good plasticizing capacity.

Algal wastewater treatment: Photoautotrophic vs. mixotrophic processes

Photoautotrophic algal systems have been investigated as potentially greener and more sustainable alternatives to the traditional bacteria-based wastewater treatment (WWT) systems. This paper presents mixotrophic algal systems as better suited for WWT. Since the literature is void of mixotrophic WWT systems, a brief review of the laboratory results from the literature comparing the different types of algal metabolisms is presented first. Details of a mixotrophic WWT system driven by an extremophilic alga, Galdieria sulphuraria (pH = 1 to 4; temperature = 25 to 56 °C) are presented next. Results from pilot scale version of this mixotrophic system (700 L) are summarized to show that it can reduce biochemical oxygen demand (BOD) and nutrients in primary-settled wastewater in a single step to yield discharge-ready effluent in <3 days of fed-batch processing. Average volumetric removal rates of BOD5 (16.5 ± 3.6 mg L−1 d−1) and ammoniacal nitrogen (6.09 ± 0.92 mg L−1 d−1) in this mixotrophic system were found to be not different from those reported for the photoautotrophic high rate algal ponds (significance level of 0.05); but, that of phosphates (1.40 ± 0.57 mg L−1 d−1) is greater than that reported for the photoautotrophic high rate algal ponds (significance level of 0.05). Additionally, the extreme culture conditions in this particular mixotrophic system enabled concurrent reductions of E. coli (>5 log) and other pathogenic bacteria.

Carbon conversion and stabilisation of date palm and high rate algal pond (microalgae) biomass through slow pyrolysis

Carbon conversion and stabilisation of date palm and high rate algal pond (microalgae) biomass through slow pyrolysis

Importance of ecological interactions during wastewater treatment using High Rate Algal Ponds under different temperate climates

Several studies focused on wastewater treatment in High Rate Algal Ponds (HRAP) suggest that highly variable climatic conditions cause large variations of microalgal biomass productivity. In the present study, we show that similar carbon, nitrogen and phosphorus removal efficiencies were reached in different HRAPs treating urban wastewaters located in two different temperate (Mediterranean and oceanic) climates. Furthermore, similar ecological successions were observed in these HRAPs. During the start-up phase, the consumption of organic matter by detritivores, already present in the wastewater, appears to be necessary for the microalgae to grow within two weeks in spring. The growth of the rapid-growing species, Chlorella sp., followed by the grazing-resilient species, Scenedesmus sp., combined with nitrifying and denitrifying bacterial activity, removed most the ammonia. The resulting exhaustion of ammonia would limit the complete removal of dissolved COD by bacteria and phosphate by microalgae in the HRAPs. This study shows that similar biological and environmental constraints were applied on the HRAPs, making the process efficiency highly reproducible under different temperate latitudes.

Bacterial communities protect the alga Microchloropsis salina from grazing by the rotifer Brachionus plicatilis

Open algal ponds are likely to succumb to unpredictable, devastating crashes by one or several deleterious species. Developing methodology to mitigate or prevent pond crashes will increase algal biomass production, drive down costs for algae farmers, and reduce the risk involved with algae cultivation, making it more favorable for investment by entrepreneurs and biotechnology companies. Here, we show that specific algal-bacterial co-cultures grown with the green alga Microchloropsis salina prevented grazing by the marine rotifer, Brachionus plicatilis. We obtained seven algal-bacterial co-cultures from crashed rotifer cultures, maintained them in co-culture with Microchloropsis salina, and used a microalgal survival assay to determine that algae present in each co-culture were protected from rotifer grazing and culture crash. After months of routinely diluting and maintaining these seven algal-bacterial co-cultures, we repeated the assay and found the opposite result: none of the seven bacterial communities protected the microalgae from rotifer grazing. We performed 16S rRNA gene amplicon sequencing on the protective and nonprotective co-culture samples and identified substantial differences in the makeup of the bacterial communities. Protective bacterial communities consisted primarily of Alphaproteobacteria (Rhodobacteraceae) and Gammaproteobacteria (Marinobacter, Pseudomonas, Methylophaga) while nonprotective bacterial communities were less diverse and missing many putatively crucial members. We compared the seven protective communities with the seven nonprotective communities and we correlated specific bacterial amplicon sequence variants with algal protection. With these data, our future work will aim to define and develop an engineered-microbiome that can stabilize industrial Microchloropsis salina cultures by protecting against grazer-induced pond crashes.

Removal of metals from water using a novel high-rate algal pond and submerged macrophyte pond treatment reactor.

A combined high-rate algal pond and submerged macrophyte pond (APMP) reactor was introduced as a novel biotechnique for efficient heavy metals (HMs) removal from wastewater. The role of water temperature, light regime, and N:P mass ratio on algae growth and HMs removal as well as effects of macrophyte species and densities on algae extermination were investigated through batch experiments. Results showed that water temperature significantly affected algae proliferation and HMs removal. Effects of light regime and N:P only showed obvious influences on HMs removal performance at high temperature. HMs removal efficiency reached 75.8% (Cr), 63.6% (Pb), and 61.1% (Zn) at 5-day hydraulic retention time (HRT) in APMP. Positive correlation existed closely between HMs removal and algal growth with long HRT. Algae were strongly inhibited by Ceratophyllum demersum and Vallisneria natans at plant density of 20-30 rhizomes m-2 with effluent algae concentration about 1,000 cells mL-1 at 7-day HRT. Results suggested that the APMP reactor was efficient for HMs removal from wastewater, indicating a possible effective metals removal technique by using APMP.

A photosynthetic toxicity biosensor for water

Effective detection of contaminants in water is the basis of safe water provision to communities. Traditional analytical methods are, however, expensive, time-consuming and cannot be easily adapted to emerging pollutants (i.e. herbicides, pharmaceuticals and their metabolites). Microalgae have been shown to be an ideal sensing probe for bioactive compounds, with great sensitivity and limit of detections at very low concentration levels (nM range). In this study, we explore the use of microalgae in microbial fuel cells (MFCs) as a means to generate a sensitive, portable and cost-effective bioelectrochemical sensor for onsite monitoring of pollutants in water. In particular, we report an innovative miniature single chamber photosynthetic MFC (photoMFC) and demonstrate its ability to detect formaldehyde, a highly toxic compound that can arise in drinking water from the oxidation of natural organic matter during ozonation and chlorination. The photoMFC, inoculated with a mixed microalgae culture from a wastewater treatment algal pond, generated a peak power and current density of 0.18 mW m−2 and 7.2 mA m−2 respectively, when exposed to light. A current response to formaldehyde proportional to its concentration was produced in less than 1 h, with a sensitivity of 69.2 ± 16.7%−1 cm−2. As such, this work provides the first miniature photosynthetic MFC device water shock sensor, with the great benefit of simple operation (with light being the sole energy source) and rapid onsite biosensing capability.

Microalgal–Bacterial Flocs and Extracellular Polymeric Substances: Two Essential and Valuable Products of Integrated Algal Pond Systems

The integrated algal pond system (IAPS) is a passive wastewater treatment technology that can be used to remediate liquid waste from domestic, industrial and agricultural sources. The system exploits the mutualistic interaction between microalgae and bacteria to generate water of a quality suitable for discharge and/or reuse. During the treatment process, biomass in the form of microalgal–bacterial flocs (MaB-flocs) is generated, and this can be harvested and beneficiated in downstream processing. Here, we review literature on MaB-floc and extracellular polymeric substance (EPS) formation and discuss how essential microalgal–bacterial mutualism is at effecting IAPS-based wastewater treatment. Aggregation of microalgae and bacteria into MaB-flocs is clearly an outcome of EPS production by these microorganisms and arises for purposes of chemical and developmental interaction, protection, communication, aggregation and adhesion. The polymeric compounds which form the scaffold of this extracellular matrix comprise polysaccharides, proteins, uronic acid and nucleic acid. Natural EPS can be used as bioflocculant in water purification and in the dewatering and settling of sludge and is therefore an ideal natural replacement for commercially available synthetic polymers. Additionally, EPS are considered high value and can be used in many commercial applications. Thus, and to ensure sustained MaB-floc production in IAPS-based wastewater treatment plants, it is important that correct levels of EPS are maintained to facilitate settling and biomass recovery. Furthermore, it is the associated environmental and operational conditions that most impact EPS production and in turn, MaB-floc formation, and quality of the final IAPS-treated water.

Bioremediation of fishpond effluent and production of microalgae for an oyster farm in an innovative recirculating integrated multi-trophic aquaculture system

Integrated multi-trophic aquaculture (IMTA) systems are a promising solution for sustainable aquaculture combining nutrient recycling with increased biomass production. An innovative land-based recirculating aquaculture system (RAS) was studied in France for a 60-day experiment. It combined a European sea bass (Dicentrarchus labrax) RAS with two other production systems: high rate algal ponds (HRAP) with natural marine polyspecific algal assemblages, and oysters in separate open tanks. The objective was the assessment of: 1) the efficiency and the stability of the microalgae bioremediation of the effluent from a fish RAS in spring and summer, 2) the abundance and the diversity patterns of the microalgae biomass for consumption in the oyster compartment of the IMTA. Silicate was added every week after the beginning of the experiment for maintaining a Si:N:P molar ratio of 10:5:1 in the HRAP to encourage the growth of diatoms. The HRAP have an overall removal efficiency of 98.6 ± 0.2% for NO3-N, 98.0 ± 0.4% for NO2-N, 97.3 ± 0.7% for NH4-N and 96.1 ± 0.6% for PO4-P, with removal rates of 335.8 ± 0.8, 23.6 ± 0.2, 30.9 ± 0.2, and 22.3 ± 0.2 mg m−2 d−1, respectively. The concentration of total suspended solid (TSS) and chlorophyll a (chl a) increased during the experiment and reached maximum values on day 46 (135.3 ± 34.7 mg TSS l−1 and 0.42 ± 0.03 mg chl a l−1) after which the microalgae collapsed due to a CO2 limitation (pH ca. 10). Sequencing analysis revealed that the microalgae community was dominated by Tetraselmis sp. from day 1 to day 16 (45.7% to 73.8% relative abundance). From day 30 to day 43 the culture was dominated by diatoms, Phaeodactylum sp. (83.4% to 98.1% relative abundance). Although the stable carbon isotope signatures confirmed that the microalgae were consumed, oysters' growth was limited in the RAS-IMTA, suggesting that oysters were under stress or not fed enough.

Technology validation of photosynthetic biogas upgrading in a semi-industrial scale algal-bacterial photobioreactor

The performance of photosynthetic biogas upgrading coupled to wastewater treatment was evaluated in an outdoors high rate algal pond (HRAP) interconnected to an absorption column at semi-industrial scale. The influence of biogas flowrate (274, 370 and 459 L h−1), liquid to biogas ratio (L/G = 1.2, 2.1 and 3.5), type of wastewater (domestic versus centrate) and hydraulic retention time in the HRAP (HRT) on the quality of the biomethane produced was assessed. The highest CO2 and H2S removal efficiencies (REs) were recorded at the largest L/G due to the higher biogas-liquid mass transfer at increasing liquid flowrates. No significant influence of the biogas flowrate on process performance was observed, while the type of wastewater was identified as a key operational parameter. CO2 and H2S-REs of 99% and 100% at a L/Gmax = 3.5 were recorded using centrate. The maximum CH4 content in the biomethane (90%) was limited by N2 and O2 desorption.

The effect of primary treatment of wastewater in high rate algal pond systems: Biomass and bioenergy recovery

The aim of this study was to assess the effect of primary treatment on the performance of two pilot-scale high rate algal ponds (HRAPs) treating urban wastewater, considering their treatment efficiency, biomass productivity, characteristics and biogas production potential. Results indicated that the primary treatment did not significantly affect the wastewater treatment efficiency (NH4+-N removal of 93 and 91% and COD removal of 62 and 65% in HRAP with and without primary treatment, respectively). The HRAP without primary treatment had higher biodiversity and productivity (20 vs. 15 g VSS/m2d). Biomass from both systems presented good settling capacity. Results of biochemical methane potential test showed that co-digesting microalgae and primary sludge led to higher methane yields (238–258 mL CH4/g VS) compared with microalgae mono-digestion (189–225 mL CH4/g VS). Overall, HRAPs with and without primary treatment seem to be appropriate alternatives for combining wastewater treatment and bioenergy recovery.

Soil sealing by algae: An alternative to plastic pond liners for outdoor algal cultivation

Commercial production of algal biofuels is currently limited by high capital costs, particularly costs of synthetic pond liners that minimize seepage of cultivation fluids, salts, and nutrients into the subsurface beneath outdoor algae cultivation facilities. Even some profitable nutraceutical companies bear the high costs of pond liners. However, studies of animal waste holding ponds and aquaculture facilities have shown that underlying soils can effectively “self-seal”, potentially eliminating the need for plastic liners. Here, we explored the potential for self-sealing with algae to provide an alternative to synthetic pond liners in unlined algae cultivation ponds. Laboratory-scale soil column experiments were used to investigate soil clogging by algae, a topic rarely discussed in the literature. Columns composed of fine sand, loamy sand, and loam soil displayed reductions in saturated hydraulic conductivity of the entire soil column of up to two orders of magnitude in response to infiltration by the alga Scenedesmus dimorphus suspended in algal culture nutrient solution at a density of 5 × 108 cells L−1. Scanning electron microscope imaging showed a dense algal layer on the surface of each soil column, thickly coating mineral grains with algal material and filling pore spaces. The algal coating was absent in samples at >3 cm depth in the soil columns, and measurements of chlorophyll content also confirmed that algal cells were mostly confined to the soil surface. In this study, the application of an algal suspension contributed significantly to soil sealing. This new application of biological sealing technology should be studied further to determine its utility and durability as an alternative to plastic liners, perhaps in conjunction with soil compaction to achieve hydraulic conductivities beneath algal production ponds that are protective of groundwater quality.

Algal biofilm ponds for polishing secondary effluent and resource recovery

In order to reduce the cost of microalgae harvesting, biofilm algal cultivations have received attention as a potential platform for algal biomass production and wastewater treatment. Two 50-L ponds containing vertically oriented geotextiles, cotton textiles, and polyethylene sheets were fed secondary effluent to examine the growth of algal biofilms. The removal of total phosphorus, PO43−-P and NO3−-N ranged from 52 to 97%, 59 to 93%, and 0 to 99%, respectively. The highest biomass productivity was 1.4 and 0.5 g m−2 day−1, and the lipid content of the attached biomass was quite low, 0.36 and 0.48%, in the cotton textile and polyethylene-baffled pond, respectively. The lipid content of the suspended biomass of the cotton textile and polyethylene pond was very low and similar (0.5%), but it increased to 13.8 and 3.4%, respectively, after a starvation period of 13 days.

РЕЦИКЛИНГ БИООТХОДОВ НА ПТИЦЕФАБРИКЕ «МИХНЕВСКАЯ»

The article deals with the problem of recycling in poultry farm Mikhnevskaya. The work program provided for the continuation of studies on the development of the system of pond preparation of sewage water in biological ponds of purification. As one of the options, the systems of BOCS ponds (biological oxidation contact stabilization ponds) and ponds with higher aquatic vegetation, as a system of posttreatment of wastewater, as well as the use of fish ponds were proposed. The development of devices that provide deeutrophication of decontaminated wastewater in the BOCS ponds was started. As measures that contributed to the improvement of water purification to be discharged into the environment, an attempt was made to introduce at the final stages of purification of the algobacterial complex, higher aquatic vegetation, and fish seed material. A survey of the poultry farm was conducted; the conditions of wastewater formation of the Mikhnevskaya poultry farm of Stupinsky district of the Moscow region were studied. Model experiments were carried out at the Mikhnevskaya poultry farm in laboratory and semi-production conditions, directly in the laboratory of the Institute at the facility. In the course of experimental studies it was found that in the ponds under the influence of algological complex of microalgae was the process of purification and disinfection of poultry wastewater. The total death of pathogenic bacteria of the E. coli group occurred on 6-11 days after the introduction of microalgae into the water of the algal pond, which does not contradict the existing developments. At the same time, there was still an increase in fish seed material, which was sufficiently provided with food and by the autumn reached a mass of 410 grams.

MS2 coliphage and E. coli UVB inactivation rates in optically clear water: dose, dose rate and temperature dependence.

Natural ultraviolet irradiance disinfection is known to play a significant role in both natural wastewater treatment systems and drinking water disinfection processes, while the influence of ultraviolet B (UVB) delivering method on sunlight disinfection outcome is still unclear. This study aims to determine the effects of environmentally relevant temperatures, UVB doses (J m-2) and dose rates (W m-2) on the inactivation and log reduction values (LRVs) of the F-RNA coliphage MS2 and Escherichia coli in optically clear water. E. coli and MS2 were separately incubated and irradiated at five different doses of UVB light that delivered using six UVB dose rates. The results of the study demonstrate that the UVB dose delivering method (combination of dose rate and exposure time) influences inactivation and LRVs of E. coli and MS2 at all UVB doses investigated (up to seven-fold difference). Two phases were identified within the UVB dose rate, UVB inactivation or LRV curves for both organisms; a UVB dose rate limited inactivation phase and a dose rate saturation inactivation phase. The results contribute to a better understanding of UVB disinfection in the environment and natural wastewater treatment systems, potentially improving the design and operation of high rate algal ponds.

Continuous low dosing of cationic polyacrylamide (PAM) to enhance algal harvest from a hectare-scale wastewater treatment high rate algal pond

ABSTRACTCationic polymers (e.g. polyacrylamide) having a high molecular weight require a much lower dose than inorganic metal salts (e.g. AlCl3, FeCl3, or Al2(SO4)3) to produce dense compact flocs with good settling characteristics. This study investigated the effect of a continuous low dosing of cationic polyacrylamide (PAM) to achieve efficient algal removal from a 1-ha High Rate Algal Pond (HRAP) treating domestic wastewater in New Zealand. Firstly, standard jar tests were conducted in laboratory conditions. A wide range of PAM dose rates (0.25–9 mg/L), mixing periods (60–250 s) and settling times (0–120 min) were tested on HRAP effluent samples to determine optimal operational parameters for the 1-ha HRAP in terms of TSS and turbidity removal. PAM addition effectively promoted flocculation of the wastewater algal biomass, removing 78% of TSS (from 135 to 30 mg/L) and 70% of turbidity (from 41 to 12 NTU) at a dose of only 4 mg/L. The jar tests determined that ∼120 s of vigorous mixing followed by 15-min of settling were sufficient to promote the formation of dense/settleable algal flocs. Continuous addition of PAM to the hectare-scale HRAP effluent at the 4 mg/L laboratory determined dose rate was found to improve TSS removal in the Algal Harvest Pond (AHP) by ∼55% (from 13% to 68%). The TSS concentration and turbidity of the AHP effluent were consistently maintained <50 mg/L and <18 NTU respectively. Furthermore, a ∼1-log E. coli removal (from 1 × 105 to 1 × 104 MPN/100 ml after settling) was also achieved in the AHP as a result of the algal floc formation and removal. Overall, this study demonstrated that addition of low levels of the chemical flocculant (e.g. cationic polyacrylamide) to the HRAP effluent can greatly improve algal solid removal (at least 50%) with a minimum chemical cost (∼$0.05 NZD/m3 of wastewater).

Impact of solids residence time on community structure and nutrient dynamics of mixed phototrophic wastewater treatment systems

Suspended growth, mixed community phototrophic wastewater treatment systems (including high-rate algal ponds and photobioreactors) have the potential to achieve biological nitrogen and phosphorus recovery with effluent nutrient concentrations below the current limit-of-technology. In order to achieve reliable and predictive performance, it is necessary to establish a thorough understanding of how design and operational decisions influence the complex community structure governing nutrient recovery in these systems. Solids residence time (SRT), a critical operational parameter governing growth rate, was leveraged as a selective pressure to shape microbial community structure in laboratory-scale photobioreactors fed secondary effluent from a local wastewater treatment plant. In order to decouple the effects of SRT and hydraulic retention time (HRT), nutrient loading was fixed across all experimental conditions and the effect of changing SRT on microbial community structure, diversity, and stability, as well as its impact on nutrient recovery, was characterized. Reactors were operated at distinct SRTs (5, 10, and 15 days) with diurnal lighting over long-term operation (>6 SRTs), and in-depth examination of the eukaryotic and bacterial community structure was performed using amplicon-based sequencing of the 18S and 16S rRNA genes, respectively. In order to better represent the microalgal community structure, this study leveraged improved 18S rRNA gene primers that have been shown to provide a more accurate representation of the wastewater process-relevant algal community members. Long-term operation resulted in distinct eukaryotic communities across SRTs, independent of the relative abundance of Operational Taxonomic Units (OTUs) in the inoculum. The longest SRT (15 days, SRT 15) resulted in a more stable algal community along with stable bacterial nitrification, while the shortest SRT (5 days, SRT 5) resulted in a less stable, more dynamic community. Although SRT was not strongly associated with overall bacterial diversity, the eukaryotic community of SRT 15 was significantly less diverse and less even than SRT 5, with a few dominant OTUs making up a majority of the eukaryotic community structure in the former. Overall, although longer SRTs promote stable bacterial nitrification, short SRTs promote higher eukaryotic diversity, increased functional stability, and better total N removal via biomass assimilation. These results indicate that SRT may be a key factor in not only controlling microalgal community membership, but community diversity and functional stability as well. Ultimately, the efficacy and reliability of NH4+ removal may be in tension with TN removal in mixed phototrophic systems given that lower SRTs may achieve better total N removal (via biomass assimilation) through increased eukaryotic diversity, biomass productivity, and functional stability.