High-rate Pond Research Articles

Influence of solar radiation on nitrogen recovery by the biomass grown in high rate ponds

The objective of this study was to assess the effect of different solar radiation intensities on nitrogen assimilation by a consortium of bacteria and microalgae grown in pilot scale high rate ponds (HRP) treating domestic wastewater. The HRPs received effluent from an anaerobic reactor. The experiment was carried out under tropical climate conditions. A total of five HRPs were used; four of them were covered with shading screens that blocked 9%, 18%, 30% and 60% of the incident solar radiation. Nitrification was the main process for nitrogen removal/transformation in all HRPs and the volatilization of ammonia nitrogen occurred in levels below the expected range due to low pH values. The organic nitrogen concentration followed the same trend of the biomass production, but no statistical difference was found between the 60% screen HRP and the uncovered one, which led to the conclusion that the intensity of the photosynthetically active radiation does not compromise nitrogen assimilation, since the bacterial biomass may develop in conditions that are unfavorable to the growth of microalgae. Moreover, other aspects, such as CO2 addition, may reduce nitrogen losses by volatilization and denitrification, as well as contribute to recover this nutrient through biomass assimilation.

Biodiesel from wastewater: lipid production in high rate algal pond receiving disinfected effluent.

The production of different species of microalgae in consortium with other micro-organisms from wastewaters may represent an alternative process, to reduce the costs, for obtaining biofuels. The aim of this study was to evaluate the influence of pre-ultraviolet disinfection (UV) in the production of lipids from biomass produced in high rate ponds. Two high rate algal ponds were evaluated: a pond that received domestic sewage without disinfection and the other receiving domestic sewage previously disinfected by UV radiation (uvHRAP). The UV disinfection did not lead to significant differences in fatty acid profile and total lipid productivities, although it increased algal biomass concentration and productivity as well as lipid content. Moreover, the overall biomass concentrations and productivities decreased with the UV disinfection, mostly as a consequence of a loss in bacterial load. We thus conclude that uvHRAP disinfection may represent a potential strategy to promote the cleaner and safer growth of algal biomass when cultivated in consortium with other micro-organisms. Mainly regarding the use of wastewater as culture medium, together with a cheaper production of lipids for biodiesel, pre-disinfection may represent an advance since extraction costs could be significantly trimmed due to the increase in lipid content.

Algae/bacteria consortium in high rate ponds: Influence of solar radiation on the phytoplankton community

Using multivariate statistical tools, the composition of the phytoplankton community was related to the characteristics of the domestic sewage used as culture medium in three high rate ponds (HRPs) submitted to different solar radiation levels. A total of 32 genera of phytoplankton were identified in the ponds; the class Chlorophyceae was the most abundant during the entire sampling period, with a larger number of individuals of the genus Desmodesmus in the summer and fall, and of the genus Chlorella in the winter and spring. The lowest occurrence of phytoplankton was observed in the fall, with behavior similar to the evolution of solar radiation throughout the year. Blocking over 30% of the solar radiation allowed for less variability of the phytoplankton community and favored the growth of biomass with higher density of individuals, as well as higher concentrations of chlorophyll-a and dissolved oxygen. On the other hand, the pond with 80% of shading presented the lowest mean density of organisms; from the perspective of wastewater treatment, however, it can be considered the most efficient in terms of organic matter and nutrient removal. According to the regression analysis, the algal biomass in HRPs can be maximized mostly if we consider the positive effect of carbon and phosphorus and the limiting effect of nitrogen and non-biodegradable organic load. For the conditions evaluated in this study, the photoinhibition phenomenon was not observed. Other aspects such as competition with other microorganisms for space and nutrients, or predation by zooplankton, seemed to be more significant for the growth and development of algal biomass.

Effect of solar radiation on the lipid characterization of biomass cultivated in high-rate algal ponds using domestic sewage

The objective of this paper is to compare the lipid content and composition of biomass produced by a consortium of microalgae and bacteria, cultivated under different solar radiation intensities and tropical conditions in pilot-scale high-rate ponds (HRPs) using domestic sewage as culture medium. The treatment system consisted of an upflow anaerobic sludge blanket reactor followed by UV disinfection and six HRPs covered with shading screens that blocked 9%, 18%, 30%, 60% and 80% of the solar radiation. The total lipid content does not vary significantly among the units, showing a medium value of 9.5%. The results show that blocking over 30% of the solar radiation has a negative effect on the lipid productivity. The units with no shading and with 30% and 60% of solar radiation blocking have statistically significant lipid productivities, varying from 0.92 to 0.96 g m−2 day−1. Besides radiation, other variables such as volatile suspended solids and chlorophyll-a are able to explain the lipid accumulation. The lipid profile has a predominance of C16, C18:1 and C18:3 acids. The unsaturation of fatty acids increases with the reduction in solar radiation. On the other hand, the effect of polyunsaturation is not observed, which is probably due to the presence of a complex and diverse biomass.

Managing the cultivation and processing of microalgae to prolong storage in water-in-oil emulsions

Producing biofuel from microalgae on a large scale will require high biomass productivity using systems such as high-rate raceway ponds. The vast scale of proposed raceway ponds, spanning 247 to 988 acres per farm, suggests practices currently used in commercial monoculture agricultural systems will need to be adopted for cultivation of algae. In commercial crop production, monoculture is facilitated by a well-established seed production, distribution, and delivery system. Currently, no such system exists for microalgae. The aims of this study were to investigate the application of water-in-oil (W/O) emulsions for the storage of microalgae and the management steps required to prolong cell viability. Water-in-oil emulsions were prepared with Chlorella sorokiniana, C. minutissima, C. vulgaris var. vulgaris, and C. vulgaris to investigate the impacts of cell cultivation medium and cell acclimation prior to emulsification on cell viability during storage. For emulsions prepared with C. sorokiniana, cells that received an acclimation treatment 24 h between cell separation from the cultivation medium and emulsification survived over 100 days longer than cells that did not receive an acclimation treatment. Emulsions prepared with C. sorokiniana grown in medium containing 29.7 mM KNO3, 1.66 mM MgSO4 · 7H2O, and 0.85 mM FeSO4 · 2H2O had higher levels of viable cells after 100 days of storage compared to cells grown in medium containing 9.90 mM KNO3 and 0.20 mM MgSO4 · 7H2O with no FeSO4 · 2H2O. The results indicate that processing of cells can be managed to increase the stability of microalgae in W/O emulsions.

Nitrification–denitrification in a coupled high rate – Water hyacinth ponds

Nitrogen transformation was studied in a coupled high rate and water hyacinth (Eichhornia crassipes) ponds at the University of Dar es Salaam. Samples of wastewater were collected and examined for water quality parameters which were used as input parameters in a mathematical model. A conceptual model was then developed to model various processes in the system using STELLA 6.0.1 software. The studGupta and Sujathay demonstrated the dominant nitrogen transformation process in high rate pond (HRP) was nitrification, but denitrification dominated in water hyacinth pond (WHP). In a HRP denitrification and volatilization accounted for 69.1% and 23.8% of removed nitrogen, respectively. On the other hand, denitrification and net sedimentation were the major nitrogen removal mechanisms in WHP accounting for 81.9% and 13.1% of removed nitrogen, respectively. Model results indicated that 1.22gN/m2day and 0.37gN/m2day of nitrogen was removed in presence and absence of biofilm, respectively. The decrease in nitrogen removal in absence of biofilm, demonstrates the importance of biofilm attached onto plants. It was concluded that incorporation of HRP improved denitrification in WHP because it enhanced formation of more nitrates in HRP in order to promote denitrification in wetland unit due to anoxic conditions.

Dynamics of Nitrogen Transformation and Removal in a Pilot High Rate Pond

The transformation and removal of nitrogen was studied in a pilot high rate pond with a surface area of 10.2 m2 and water depth of 60 cm. The pilot unit received wastewater from an existing field scale primary facultative pond at the University of Dar es Salaam. Wastewater samples were collected from the influent and effluent of high rate pond and were analyzed for physical-chemical parameters in the laboratory and in situ. An appropriate model complexity was selected, from which a conceptual model was then developed to model various processes in the system using STELLA 6.0.1 software. The study demonstrated that dominant nitrogen transformation processes in HRP were nitrification and denitrification, which transformed 0.95 and 0.87 gN/m2·d, respectively. These were followed by mineralization (0.37 gN/m2·d), ammonia uptake by microorganisms (0.34 gN/m2·d), volatilization (0.30 gN/m2·d), sedimentation (0.24 gN/m2·d), and regeneration (0.15 gN/m2·d). Uptake of nitrate was not observed because of microorganisms preference for ammonia, which was abundant in the pond. The major nitrogen transformation mechanisms in high rate pond were denitrification, net sedimentation and volatilization, which accounted for 69.1%, 7.1% and 23.8% of the total permanent removal mechanisms of nitrogen in High Rate Pond.

Differentiation criteria study for continuous stirred tank reactor and plug flow reactor

All reactors in reality are not ideal plug flow reactor (PFR) or ideal continuous stirred tank reactor (CSTR). They are difficult to differentiate. This study was to investigate the reactor analysis of PFR and CSTR through tracer response curves, residence time distributions (RTD) and several hydraulic performance indexes. We set up the differentiated value of each index. The tracer response curve showed that our lab-scale CSTR was close to ideal CSTR and got 99.9% recovery. In the RTD curves, the results could significantly recognize the PFR nature of high rate pond (HRP). With hydraulic performance indexes study, every selected index demonstrated that the studied HRP was closer to PFR than the studied CSTR. Based on the lab-scale study results, this study established the cutting point between the PFR and CSTR in each index; we were looking through the different types of reactors in literature and we confirmed the criteria with all literature reactors with the “graphic method”. The method helped us to establish those important values to help us to differentiate the reactor types in practice and to understand the designs better.

Long-term anaerobic digestion of microalgae grown in HRAP for wastewater treatment. Effect of microwave pretreatment

This paper describes the anaerobic digestion of microalgal biomass from high rate ponds in continuous anaerobic reactors for biogas production. With hydraulic retention times (HRT) of 15 and 20 days, the volatile solids (VS) removal did not exceed 30%, and the methane production rate ranged between 0.12 and 0.14 L CH4/L day. To improve process performance, microwave irradiation at 900 W for 3 min (specific energy ∼70,000 kJ/kg VS) was applied as a pretreatment step. The VS removal increased to 40 and 45% at 15 and 20 days HRT, respectively. Consequently, the methane production rate increased to 0.16 and 0.20 L CH4/L day at 15 and 20 days HRT, respectively. Microscopic analysis confirmed cell wall damage, although generally without lysis, after irradiating microalgal biomass. However, the energy consumption was much higher than the extra energy production of the process. Indeed, microalgal biomass should not only be thickened but also dewatered if microwave irradiation was to be applied as a pretreatment to anaerobic digestion for biogas production.

<i>Arthrospira</i> (Spirulina) in tannery wastewaters Part 1: The microbial ecology of tannery waste stabilisation ponds and the management of noxious odour emissions using microalgal capping

We investigated the problem of noxious gas and odour emissions in zero-discharge evaporative tannery waste stabilisation ponds. These have been little-studied systems although they present one of few options for the management of tannery wastewaters in highly water-stressed areas. A three-year study of the microbial ecology of an evaporative waste stabilisation ponding cascade was undertaken and a descriptive account of the biology and the physico-chemical parameters related to odiferous gas release is reported. Large populations of Arthrospira (Spirulina) dominated the latter facultative ponds in the cascade where odour emission was substantially reduced compared to initial anaerobic ponds. Photosynthetic productivity maxima of up to 9 000 mg∙m-2∙day-1 carbon fixation were measured in bloom conditions. Arthrospira production was associated with an oxygenated, alkaline layer established on the surface of facultative ponds (0.35 m in depth) in which oxidation of sulphide and ammonia, and the trapping of other odour-causing compounds was observed. An attempt was made to achieve comparable odour control in the anaerobic ponds by capping with recirculated microalgae-enriched effluent from facultative ponds. While this was shown to be effective in establishing an Arthrospira-dominant surface layer and an associated control of odour emissions in anaerobic ponds, large recirculation volumes (2:1) were required to maintain the Arthrospira population. Elevated salinity of recirculated facultative pond waters also negatively impacted the evaporative function in the low-salinity initial ponds in the cascade. An alternative method of Arthrospira capping was investigated which involved the construction of a free-standing high rate pond alongside the waste stabilisation pond system, and using a controlled feed of raw tannery effluent for optimising the cultivation of Arthrospira biomass. High biomass productivity was achieved in this unit (12.87 g∙m-2∙day-1), using a low feed to effluent loading volume ratio (0.21:1) and subsequent capping of anaerobic ponds from this source achieved odour control comparable to facultative ponds. This study has shown that management of the odour problem in waste stabilisation ponds is possible and that leather production using the zero-discharge evaporative disposal operation may be compatible with a level of both environmental and social acceptability of these systems. Odour problems, alone, should thus not constrain tanning as one of the few industrial agricultural activities available in rural economies.Keywords: tannery, wastewater, waste stabilisation ponds, odour, noxious gas, Spirulina, Arthrospira, microalgal biomass

A high rate ponding unit operation linking treatment of tannery effluent and Arthrospira (Spirulina) biomass production. 1: Process development

Effluent from the production of wet blue leather has been shown to support the substantial growth of Arthrospira biomass in tannery waste stabilization ponds, which is of interest in its use both in animal feeds and biofuels production. Here we report process development investigations which were undertaken in photobioreactor and outdoor high rate pond pilot studies. Biomass productivities of 16 t ha−1 yr−1 (dry mass) were measured which compares broadly with yields reported for Arthrospira cultivated in other complex media. The specific growth rate μ = 0.05 d−1 was somewhat lower than reports for the mixotrophic cultivation of Arthrospira in defined media studies. This system operates under ammonia control and may be relieved by recirculation of alkaline waters which accumulate in these waste stabilization ponds. A substantial difference in total nitrogen and phosphorus removal between the experimental and theoretical yields due to biological activity suggests stripping may account for the largest fraction of ammonia removal, and precipitation for phosphate removal, in this operation. Heavy metal contamination may be a problem with biomass production in industrial effluents and pretreatment of the tannery effluent in a primary facultative pond was shown to substantially reduce the heavy metal load. Process kinetic values were derived and have been used for the design and construction of a full-scale Arthrospira production operation using tannery effluent growth media, which is reported in a follow-up study.

Growth condition study of algae function in ecosystem for CO 2 bio-fixation

Algae niche play a crucial role on carbon cycle and have great potential for CO 2 sequestration. This study was to investigate the CO 2 bio-fixation by the high rate pond (HRP) to mimic the algae function of nature. All the reactors can keep CO 2 consumption efficiencies over 100%. The statistical analyses proved HRPs were close to the natural system from all the growth conditions. The HRP could show the “natural optimization as nature” to perform as well as the artificial reactor of continuously stirred tank reactor (CSTR). In the nutrition study, the carbon mass balance indicated CO 2 was the main carbon source. Accordingly, the HRPs can keep a neutral pH range to provide dissolved oxygen (DO), to promote total nitrogen (TN)/total phosphorous (TP) removal efficiencies and to demonstrate self-purification process. Furthermore, the observations of different nitrogen species in the reactors demonstrated that the major nitrogen source was decided by pH. This finding logically explained the complex nitrogen uptake by algae in nature. Consequently, this study took advantage of HRP to explore the processes of efficient CO 2 uptake with the corresponding growth condition in the ecosystem. Those results contributed the further understanding of the role of CO 2 bio-fixation in nature and demonstrated HRP could be a potential ecological engineering alternative.

Advances in Wastewater Treatment Pond Performance Using High Rate Ponds

Advances in Wastewater Treatment Pond Performance Using High Rate Ponds

Pilot Research on Nutrient Removal with CO<SUB>2</SUB> Supplemented Algal High Rate Ponds

Pilot Research on Nutrient Removal with CO2 Supplemented Algal High Rate PondsA concept for achieving biological nutrient removal in high rate algal ponds supplemented with CO2-rich flue gas is under development, including small-scale pilot work described herein. The potential advantages of such an Algal Nutrient Removal (ANR) system compared to conventional mechanical treatment technologies, such as activated sludge, include lower capital and operating costs, a lower...Author(s)Tryg LundquistIan WoertzPaul WardSourceProceedings of the Water Environment FederationSubjectSession 32: Algae: State of the IndustryDocument typeConference PaperPublisherWater Environment FederationPrint publication date Jan, 2010ISSN1938-6478SICI1938-6478(20100101)2010:15L.1874;1-DOI10.2175/193864710798159200Volume / Issue2010 / 15Content sourceWEFTECFirst / last page(s)1874 - 1880Copyright2010Word count152Subject keywordsAlgaepondswastewater treatmentnutrient removalCO2

Nutrient Removal & Greenhouse Gas Abatement with CO2 Supplemented Algal High Rate Ponds

High rate algae ponds fed clarified domestic wastewater and CO2-rich flue gas are expected to remove nutrients to concentrations similar to those achieved in mechanical treatment technologies, such as activated sludge. However, the energy intensity of wastewater treatment with CO2-supplemented high rate ponds (HRPs) would be less than that of mechanical treatments. In conjunction with anaerobic digestion of algal biomass and co-substrates, the algae-based system would produce a substantial excess of electricity. Greenhouse gas abatement from such CO2-HRP/digestion systems would stem mainly from energy conservation and the offset of fossil fuel electricity with biogas-derived electricity. Laboratory experiments showed nutrient removals of >98% for ammonium and >96% for phosphorus with mixed culture microalgae grown on CO2-supplemented primary wastewater effluent. An engineering numerical model for CO2-HRP/digestion facilities (based in part on large-scale algae production under southern California conditions) indicates a potential energy surplus of 330 kWh/ML (1,200 kWh/MG) from biogas-derived electricity, compared to the net energy consumption of about 760 kWh/ML (2,900 kWh/MG) at typical activated sludge facilities with nitrification/denitrification. Considering the net electricity production and energy savings of the CO2-HRP/digestion systems, a greenhouse gas abatement potential of 660 kg CO2eq/ML (2,500 kg CO2eq/MG) treated is expected for a 100-ha facility treating 20 MGD.

Nutrient Removal & Greenhouse Gas Abatement with CO2 Supplemented Algal High Rate Ponds

Nutrient Removal & Greenhouse Gas Abatement with CO₂ Supplemented Algal High Rate Ponds

Influence of CO2 scrubbing from biogas on the treatment performance of a high rate algal pond

Biogas produced by anaerobic treatment of wastewater can be collected and used for power generation. However, the biogas may require scrubbing to prevent corrosion by H2S and to improve engine efficiency by reducing the CO2 content. HRAP can be used to scrub biogas during the daytime when they are carbon-limited and have high pH. This study investigates the influence of the carbon dioxide addition from biogas scrubbing on high rate algal pond wastewater treatment performance (in terms of BOD, NH4-N, DRP and E. coli removal) and algal production (growth and species composition). Batch culture experiments were conducted in laboratory microcosms (2 L) and outside mesocosms (20 L). Results indicate that CO2 addition and reduced culture pH increased algal production and nutrient assimilation, decreased high pH mediated nutrient removal processes (phosphate precipitation and ammonia volatilisation), but had little influence on the ability of the culture to remove filtered BODs. Disinfection, as indicated by E.coli removal; was reduced, however, further research on virus removal, which is not affected by culture pH, is required. These preliminary findings indicate the potential to scrub C02 from biogas using high rate pond water without decreasing the effectiveness of wastewater treatment and enabling increased recovery of wastewater nutrients as algal biomass.

Food inputs, water quality and nutrient accumulation in integrated pond systems: A multivariate approach

A participatory on-farm study was conducted to explore the effects of food input patterns on water quality and sediment nutrient accumulation in ponds, and to identify different types of integrated pond systems. Ten integrated agriculture–aquaculture (IAA) farms, in which ponds associate with fruit orchards, livestock and rice fields were monitored in the Mekong delta of Vietnam. Pond mass balances for nitrogen (N), organic carbon (OC) and phosphorus (P) were determined, and pond water quality and sediment nutrient accumulation were monitored. Data were analyzed using multivariate canonical correlation analysis, cluster analysis and discriminant analysis. The main variability in pond water quality and sediment nutrients was related with food inputs and water exchange rates. Water exchange rate, agro-ecological factors, pond physical properties and human waste input were major variables used to classify ponds. Classification was into: (1) low water exchange rate ponds in the fruit-dominated area, (2) low water exchange rate ponds in the rice-dominated area receiving homemade feed, and (3) high water exchange rate ponds in the rice-dominated areas receiving wastes. Pond water exchange rate was human-controlled and a function of food input patterns, which were determined by livelihood strategies of IAA-households. In the rice-dominated area with deep ponds, higher livestock and human wastes were found together with high water exchange rates. In these ponds, large organic matter loads reduced dissolved oxygen and increased total phosphorus concentrations in the water and increased nutrient (N, OC and P) accumulation in the sediments. In the rice-dominated area with wide ponds, higher homemade feed amounts were added to the ponds with low water exchange rate. This resulted in high phytoplankton biomass and high primary productivity. The contrary occurred in the fruit-dominated area, where fish were grown in shallow and narrow ponds, receiving more plant residue which resulted in lower phytoplankton biomass and lower sediment nutrient accumulation.

Long term diurnal variations in contaminant removal in high rate ponds treating urban wastewater

In this investigation, diurnal variations in contaminant removal in high rate ponds (HRP) treating urban wastewater were evaluated. Two experimental HRPs (surface area 1.54 m 2 and depth 0.3 m), each with a clarifier in series (surface area 0.025 m 2), were operated in parallel with different hydraulic retention times (3–10 days) but with the same environmental conditions over a period of one year. The operating strategies adopted only yielded a significant overall difference in removal between the two HRPs for nutrients. Effluent total suspended solids and chemical oxygen demand were slightly higher at midday than at dawn, while for total nitrogen and total phosphorous the concentrations were slightly higher at dawn. All these differences were related to the diurnal changes of DO and pH. The main conclusion of this work is that the diurnal variations of the contaminant concentrations in HRPs do not seriously affect their reliability in treating wastewater.

Potential biogas scrubbing using a high rate pond

The potential to scrub biogas in a high rate pond (HRP) was evaluated using apparatus designed to maximize gas-liquid contact. Experiments compared the removal of carbon dioxide from synthetic biogas by an "in-pond angled gutter" to that by a simulated "counter-current pit." Results showed that the counter current pit has potential for use in biogas scrubbing, with synthetic biogas carbon dioxide composition consistently reduced from 40% to < 5%. The in-pond angled gutter was less effective due to bubble coalescence which reduced the total bubble surface area available for gas transfer. Measurement of oxygen levels in the scrubbed biogas showed that despite supersaturation of oxygen in the HRP water, there was little transfer to the biogas, so that explosive methane/oxygen mixtures would not be formed. Theoretical calculations indicated that the amount of biogas likely to be formed during anaerobic treatment of municipal wastewater could be scrubbed in the HRP of the same advanced pond system with little influence on HRP pH, algal growth and treatment performance. These encouraging results justify further research on this method of biogas purification.