The effect of bacterial contamination on the heterotrophic cultivation of Chlorella pyrenoidosa in wastewater from the production of soybean products

This study examined the impacts of bacteria on the algal biomass, lipid content and efficiency of wastewater treatment during the heterotrophic cultivation of Chlorella pyrenoidosa. Our results showed that soybean-processing wastewater can enhance the accumulation of lipids in algal cells and thus raise the lipid yield in the pure culture. The bacteria coexisting with algae improved the degradation of total nitrogen (TN), total phosphorus (TP), glucose and chemical oxygen demand (COD). Although the biomass productivity of algae was not significantly affected, the total algal lipid content and lipid production rate were slightly reduced when bacteria coexisted with algae. The difference in the compositions of the medium is presumed to be the main contributing factor for the variation in total lipid content in presence and absence of bacteria. The TN, TP, and COD decreased during the assimilatory process undertaken by C. pyrenoidosa, and the removal efficiency of TN by bacteria depended on the type of nitrogen species in the medium. Additionally, the apparent interaction between the bacterial and algal cultures varied with the changes in experimental conditions. Algae could compete with bacteria for the carbon and energy sources, and inhibit the growth of the bacteria in the presence of high organic matter concentration in the medium.     

Modification, calibration and verification of the IWA River Water Quality Model to simulate a pilot-scale high rate algal pond

We implemented the IWA River Water Quality Model No. 1 (Reichert et al., 2001. River Water Quality Model No. 1, IWA Scientific & Technical Report No. 12) to simulate water-quality characteristics in two pilot-scale High Rate Algal Ponds. Simulation results were compared with two years' of data from the ponds. The first year's data from one pond were used for model calibration; the remaining data were used for validation. As originally formulated and parameterized, the model consistently yielded summer-time algal biomass concentrations which were too low - with consequent failures in its reproduction of dissolved oxygen, pH and nutrient dynamics. We experimented with various structural/parametric changes to improve the model's performance. The most effective strategy was to greatly increase the respiratory losses suffered by the heterotrophic osmotrophs (thereby giving the algae access to a larger fraction of the incoming dissolved organic carbon and nitrogen). This suggests that CO₂-bubbling alone cannot entirely preclude resource-limitation of algal production. We doubt that our parameterization of heterotrophic osmotrophs is correct and infer that the algae derive a large fraction of their nutrition by direct osmotrophic uptake of dissolved organic matter. This inference is supported by the literature concerning the physiology of the dominant algal species in our ponds.     

Inorganic nitrogen removal in a combined tertiary treatment—marine aquaculture system—I. Removal efficiences

The increasing awareness that nitrogen is often a key nutrient controlling algal growth in coastal marine waters has led to a concerted effort to find ways to remove ammonia and nitrate from wastewaters. A novel approach to this problem involves the combining of algal and seaweed nutrient stripping processes with a marine aquaculture. Not only is nitrogen removed from wastewater, but important commercial shellfish and seaweeds are produced.A prototype process consisting of growth systems for marine algae, oysters and seaweed, joined in series, was fed secondarily treated wastewater, diluted 1:4 with seawater, for 11 weeks during the Summer of 1972. During this time 95 per cent of the influent inorganic nitrogen was removed by algal assimilation. The oysters in turn removed 85 per cent of the algae, but regenerated as soluble ammonia 16–18 per cent of the nitrogen originally bound in the algal cells. All of the regenerated nitrogen was removed in the seaweed system so that the total inorganic nitrogen removal efficiency of the system was 95 per cent. Phosphorus removal on the other hand was not nearly as complete as only 45–60 per cent was removed.The process has the capability of being expanded to include additional trophic levels in an integrated and highly controlled food chain system to serve the dual function of tertiary wastewater treatment and waste recycling through the production of shellfish and seaweeds.     

Productivity and nitrogen balance in large scale phytoplankton cultures

Biomass production and nitrogen balance was studied in 35,000 gal (133,000 1) phytoplankton cultures comprising the first stage in a tertiary sewage treatment-mariculture system. The diatom Phaeodactylum tricornutum persisted for most of the study. At secondary sewage effluent loadings sufficient to produce residual dissolved inorganic nitrogen concentrations above approximately 5 μg atoms l⁻¹, an N:C ratio (molar) of 0.17 was obtained and algal growth was not nutrient-limited. Biomass levels, and hence pond particulate carbon and nitrogen output, varied in response to solar irradiance and dilution rate, but not temperature. Mean winter and summer yields were approximately 1 and 5 g (83 and 417 mg atoms) C m⁻² d⁻¹ respectively. An inverse relationship existed between algal biomass concentration and dilution rate, such that in the late spring optimal pond yields occurred between 0.55 and 0.65 dilutions d⁻¹. Better than 95% dissolved total nitrogen removal was obtained. Net dissolved organic nitrogen production, that would offset dissolved inorganic nitrogen removal, did not occur. Pond particulate nitrogen output was usually less than dissolved total nitrogen removal. Probable explanations for this include (1) ammonia evolution to the atmosphere at high pond pH, (2) particulate nitrogen sedimentation, and (3) denitrification. Of these, the first is believed to be quantitatively the most significant.     

Waste activated sludge fermentation: Effect of solids retention time and biomass concentration

Laboratory scale, room temperature, semi-continuous reactors were set-up to investigate the effect of solids retention time (SRT, equal to HRT hydraulic retention time) and biomass concentration on generation of volatile fatty acids (VFA) from the non-methanogenic fermentation of waste activated sludge (WAS) originating from an enhanced biological phosphorus removal process. It was found that VFA yields increased with SRT. At the longest SRT (10 d), improved biomass degradation resulted in the highest soluble to total COD ratio and the highest VFA yield from the influent COD (0.14 g VFA-COD/g TCOD). It was also observed that under the same SRT, VFA yields increased when the biomass concentration decreased. At a 10 d SRT the VFA yield increased by 46%, when the biomass concentration decreased from 13 g/L to 4.8 g/L. Relatively high nutrient release was observed during fermentation. The average phosphorus release was 17.3 mg PO₄-P/g TCOD and nitrogen release was 25.8 mg NH₄-N/g TCOD.     

A sustainable, carbon neutral methane oxidation by a partnership of methane oxidizing communities and microalgae

Effluents of anaerobic wastewater treatment plants are saturated with methane, an effective greenhouse gas. We propose a novel approach to treat such effluents using a coculture of methane oxidizing communities and microalgae, further indicated as methalgae, which would allow microbial methane oxidation with minimal CO₂ emissions. Coculturing a methane oxidizing community with microalgae in sequence batch reactors under continuous lightning yielded a factor of about 1.6 more biomass relative to the control without microalgae. Moreover, 55% less external oxygen supply was needed to maintain the methane oxidation, as oxygen was produced in situ by the microalgae. An overall methane oxidation rate of 171 ± 27 mg CH₄ L⁻¹ liquid phase d⁻¹ was accomplished in a semi-batch setup, while the excess CO₂ production was lower than 1 mg CO₂ L⁻¹ d⁻¹. Both nitrate and ammonium were feasible nitrogen sources for the methalgae. These results show that a coculture of microalgae and methane oxidizing communities can be used to oxidize dissolved methane under O₂-limiting conditions, which could lead to a novel treatment for dissolved methane in anaerobic effluents.     

Detergent phosphorus and algal growth

The total biomass of Chlorella pyrenoidosa (two strains) Chlamydomas reinhardtii. Euglena gracilis. Anabaena flos-aquae and Plectonenema boryanum was determined after the algae were grown in waters from Sylvan, Pleasant and Pidgeon Lakes (all in northeastern Indiana) that had been supplemented with 0.1, 1 or 10% sewage effluents (Indianapolis and Crawsfordsville, Indiana). Biomass was found not to be significantly decreased when the total phosphorus was reduced by alkaline treatment from 7.20-3.50 mg l⁻¹ (50 per cent reduction) for the Crawfordsville effluents. In another series of experiments Chlorella pyrenoidosa was grown in Sugar Creek water (west central Indiana) to which had been added 0.1. 1 or 10% sewage effluents that originated from a motel treatment system. Reactive sewage phosphorus was reduced from 15.4 to 7.44 mg l⁻¹ (57 per cent reduction) by supplying the motel with non-phosphorus cleaning products. No significant reduction in algal growth was observed. Only when effluents were advanced treated so that reactive phosphorus levels were below 1.2 mg l⁻¹ (92 per cent reduction) was algal growth significantly decreased.     

Effects of whole lake mixing on water quality and phytoplankton

This paper describes the effect of artificial mixing of two Oklahoma lakes with a downflow pump on water quality and algal biomass. Artificial pumping in Arbuckle Lake (951 ha), advanced autumnal turnover, but never destratified the lake completely. Ammonia decreased in the epilimnion, while sulfide (H₂S) declined and dissolved oxygen (DO) increased in the hypolimnion. Other water quality parameters did not change. Near-bottom concentrations of manganese (Mn²⁺) increased, indicating pumping did not affect water chemistry near deep sediments (> 16 m). Pumping did not change significantly the depth of the Secchi disc or algal biomass as measured by chlorophyll a. The algal flora was dominated by diatoms at all times, and the density of blue-green algae was always low. Pumping kept Ham's Lake (41 ha) destratified, but seldom produced completely isothermal conditions or isochemical concentrations of DO. There was no drastic change in other water quality parameters. However, artificial mixing decreased water clarity and increased algal biomass by a factor of about 2.5, probably by reducing sinking rates of the phytoplankton. Artificial mixing apparently eliminated a fall pulse of Microcystis.     

The identification of phosphorus as a growth-limiting nutrient in lough neagh using bioassays

Algae were used in monthly bioassays of Lough Neagh water to evaluate nutrient limitation. Blue-green algae were limited by chelated iron; but once this limitation was overcome both nitrogen and phosphorus were necessary to produce a large growth response. The green alga Selenastrum showed a low requirement for chelated iron. Addition of phosphorus was necessary in all bioassays for prolonged algal growth, confirming the strategy of removing phosphorus from sewage effluents to reduce algal levels in the Lough.     

Hyperconcentrated cultures of Scenedesmus obliquus: A new approach for wastewater biological tertiary treatment?

Algal cultures of Scenedesmus obliquus at low concentrations (0.1–0.2 g dry wt l⁻¹) provide adequate biological tertiary treatment of wastewaters. This research was aimed at studying the possibility of increasing the system performance by using hyperconcentrated cultures of S. obliquus (up to 2.6 g dry wt l⁻¹) at the laboratory scale. The algal culture grown on secondary effluent was first chemically flocculated with chitosan (30 mg l⁻¹) and decanted; the sedimented culture (5 g dry wt l⁻¹) was then resuspended in secondary effluent to obtain algal suspensions at various concentrations, the performance of which was compared to that of a control culture (0.13 g dry wt l⁻¹). The rate of exhaustion of nitrogen (N-NH₄⁺) was proportional to the algal concentration and a complete removal could be obtained within 15 min (at 2.6 g dry wt algae l⁻¹); this result compares favorably to the 2.5 h or so required by the control culture. The unit uptake rate for nitrogen (N-NH₄⁺) had a tendency to increase with the algal concentration, whereas that of phosphorus (P-PO₄³⁻) showed the opposite relationship. Considering the results obtained, it appears that hyperconcentrated algal cultures have a high potential for the tertiary treatment of wastewaters; a significant reduction of pond surface for large scale operations can be anticipated.     

Removal of nitrogen from industrial wastewaters with the use of algal rotating disks and denitrification packed bed reactor

An attempt was made to use an algal rotating disk system in a two-step biological purification of nitrogen fertilizer industry wastewaters. The proposed method involved the removal of ammonium by Stichococcus bacillaris growing on the rotating disk and of oxidized forms of nitrogen by denitrifying bacteria. The use of a rotating algal disk followed by denitrification bed as the second step of biological treatment removed about 90% of nitrogen from the wastewater. A change of purification sequence resulted in the appearance of NO ⁻₃ and NO⁻₂ in the purified wastewater caused by the activity of nitrifying bacteria accompanying algae in the biological film on the disk. It was found that methanol used as a carbon source for denitrifying bacteria could be replaced by organic matter of algal origin.     

Phosphorus removal in the activated sludge process

The results from this research suggest that both calcium phosphate precipitation and enhanced biological uptake play a role in phosphorus removal in the activated sludge process when a non-nitrifying, anaerobic-aerobic system is used to treat a low calcium wastewater. The primary removal mechanism was found to be biological uptake, as calcium phosphate precipitation accounted for only 15–27% of the total phosphorus removed. Calcium phosphate precipitation in the aerobic unit was enhanced because of the pH increase in that reactor. This was the result of low CO₂ production (indicated by low specific oxygen uptake values) and intense aeration which caused excessive CO₂ stripping in the aerobic unit     

Removal of nitrogen, phosphorus and COD from waste water using sand filtration system with Phragmites Australis

The removal efficiencies of nitrogen, phosphorus and COD from waste water were examined using sand filtration systems with Phragmites australis (Cav.) Trin. ex. Steudel. The quality of effluent waters from the system with plant were far better than those from the one without plant, implying Phragmites could incorporate nitrogen and phosphorus into its tissues and promote phosphorus absorption onto the sand by the release of oxygen from the roots. The P-pot provided with the influent containing 198 mg l^- of total nitrogen and 21 mg l^-1 of total phosphorus had the highest biomass of Phragmites. Harvestable above-ground biomass accounted for about 3.5 kg m^-2 and removable nitrogen and phosphorus accounted for 69 and 6 g m^-2 respectively.The removal rates of total nitrogen and phosphorus in the system with Phragmites receiving variable amounts of COD were almost at the same level and also much better than those of the systems without plant, implying that the different COD concentrations in the influent media do not impair the removal efficiencies of nitrogen and phosphorus. Also Phragmites was found to resist COD concentration as high as 128 mg l^-1, and signs of clogging were not detected in this system throughout the experiment.     

Phosphorus and nitrogen removal with minimal COD requirement by integration of denitrifying dephosphatation and nitrification in a two-sludge system

Denitrifying dephosphatation enables the removal of phosphorus and nitrogen with minimal use of COD, minimal oxygen consumption and minimal surplus sludge production. Moreover it would make aeration only necessary for nitrification. Therefore we have studied an anaerobic-anoxic (A₂) sequencing batch reactor (SBR) coupled to a nitrification SBR. Denitrifying phosphorus removing bacteria (DPB) and nitrifiers were completely separated in two sludges in these two SBRs. The nitrified supernatant was recirculated from the nitrification SBR to the A₂ SBR where nitrate was utilized by DPB as an electron acceptor for phosphorus removal. The technical feasibility for simultaneous phosphorus and nitrogen removal in the proposed two-sludge system was evaluated. The benefits of two-sludge systems over single-sludge systems were also discussed. It could be concluded that the separation of the nitrification step leads to an optimal process design for the application of denitrifying dephosphatation. The two-sludge system showed stable phosphorus and nitrogen removal, and enabled the removal of 15 mg-P/1 and 105 mg N/1 at the expense of only 400 mg-COD/1 acetic acid. Stoichiometric calculations showed that, in the two-sludge system the required COD can be up to 50% less than for conventional aerobic phosphorus and nitrogen removal systems. Moreover oxygen requirements and sludge production can be decreased in significant amounts of about 30 and 50%, respectively.     

Recycling algae to improve species control and harvest efficiency from a high rate algal pond

This paper investigates the influence of recycling gravity harvested algae on species dominance and harvest efficiency in wastewater treatment High Rate Algal Ponds (HRAP). Two identical pilot-scale HRAPs were operated over one year either with (HRAP_r) or without (HRAP_c) harvested algal biomass recycling. Algae were harvested from the HRAP effluent in algal settling cones (ASCs) and harvest efficiency was compared to settlability in Imhoff cones five times a week. A microscopic image analysis technique was developed to determine relative algal dominance based on biovolume and was conducted once a month. Recycling of harvested algal biomass back to the HRAP_r maintained the dominance of a single readily settleable algal species (Pediastrum sp.) at >90% over one year (compared to the control with only 53%). Increased dominance of Pediastrum sp. greatly improved the efficiency of algal harvest (annual average of >85% harvest for the HRAP_r compared with ∼60% for the control). Imhoff cone experiments demonstrated that algal settleability was influenced by both the dominance of Pediastrum sp. and the species composition of remaining algae. Algal biomass recycling increased the average size of Pediastrum sp. colonies by 13-30% by increasing mean cell residence time. These results indicate that recycling gravity harvested algae could be a simple and effective operational strategy to maintain the dominance of readily settleable algal species, and enhance algal harvest by gravity sedimentation.     

Algal settling ponds contribute to final effluent quality of integrated algal pond systems for municipal sewage treatment

Appropriate wastewater technologies and sound management are crucial to global water quality and conservation. The integrated algal pond system (IAPS), considered an efficient, passive and low-cost wastewater treatment technology for peri-urban spaces, is perceived to yield a final effluent unsuitable for discharge. Experiments were carried out to challenge the prevailing perception that algal-based wastewater treatment processes and in particular IAPS produce an effluent that does not always meet national and/or regional regulatory standards. Formation of a microalgal–bacterial floc (MaB-flocs) and settleability together with biomass removal from algal settling ponds (ASPs) is shown to reduce total suspended solids (TSS) from >50 to <20 mg L⁻¹. Thus, production of a readily settleable MaB-floc coupled with removal of settled biomass from ASP ensures that final effluent TSS remains below the general limit of 25 mg L⁻¹ and yields an effluent suitable for either irrigation or discharge.     

Aquacultural approaches to recycling of dissolved nutrients in secondarily treated domestic wastewaters—I Nutrient uptake and release by artificial food chains

Wastewater based artificial food chains composed of sequential monocultures of a suspended unicellular green alga, of an herbivorous cladoceran crustacean, and of an herbivorous or a carnivorous teleost fish and of filamentous green algae were studied in an effort to find efficient, potentially economically viable mechanisms for the biological capture (tertiary treatment) of nutrients (especially nitrate and phosphate) in wastewaters processed by small to medium size two-stage treatment plants that primarily handle domestic and agricultural wastes.All experiments were carried out on laboratory scale systems with a low technology approach to keep apparatus and procedures as simple and reliable as possible.Among all organisms tested as components of the artificial food chains only the unicellular green alga Scenedesmus, the filamentous green algae Cladophora and Ulothrix, the cladoceran crustaceans Daphnia magna and Daphnia pulex, and the teleost fishes Notemigonus crysoleucas, Pimephales promelas and Notropis lutrensis were found to be suitable.Unmodified secondarily treated domestic effluents were both iron deficient and lacking in buffering capacity necessary for optimal algal growth. Additions of both ferrous iron (1 ppm) and carbon dioxide (5%) were required to achieve good quality cultures suitable for feeding cladocerans. Most removal of nutrients occurred in the first algal stage of the food chain. Nitrate removal averaged 78%, phosphate removal 55% in buffered algal cultures. In unbuffered cultures nitrate removal was 30%, phosphate removal 98%. The near complete removal of phosphate in unbuffered algal cultures was probably due to physico-chemical precipitation of phosphate complexes formed as a result of high pH levels (pH > 10) reached within 24 h of culture initiation. Cladoceran and fish stages added nutrients (mostly ammonia and phosphate) back into the effluent. A final stage of Ulothrix and Cladophora algae removed nutrients regenerated by cladocerans and fishes. A 12 h light–12 h dark cycle statistically significantly reduced levels of nutrient removal by both unbuffered and buffered algal cultures below removal rates measured in algae cultured in continuous light. Daily harvesting rates of 25–75% of culture volumes had no significant effect upon removals of nitrate by buffered algal cultures; phosphate removals were inversely proportional to harvesting rates in these cultures.Important theoretical and technical points are discussed.     

磷及环境因子对太湖梅梁湾藻类生长及其群落影响

在太湖梅梁湾进行的围隔试验表明,藻类生长与水华形成受气候(如水温、风浪)与营养因子(如N,P)影响。统计分析发现各点硝态氮均与叶绿素a显著负相关,在不同围隔中水温、总磷、总氮等与叶绿素a显著相关。各围隔中优势种主要为蓝藻,尤其是微囊藻类。加磷对藻类生长与群落结构均有影响,但磷营养不是目前太湖水华爆发的关键因素。     

The occurrence and removal of nitrogen in subsurface agricultural drainage from the San Joaquin Valley, California

During the years 1967–1973 there have been extensive studies of subsurface agricultural drainage in the San Joaquin Valley of California. These studies, by cooperating state and federal agencies, were to determine the composition and quantity of drainage waters produced from irrigated agriculture, to evaluate possible methods of removing problem constituents (mainly nitrogen) from these waters, and to obtain an idea of the effectiveness of the treatment methods studied for reducing the waters biostimulatory content with respect to potential receiving waters. The results of the studies indicated that on an annual average, the drainage waters will probably contain about 20 mg NO₃-N I⁻¹ even after 50 years of leaching and that most of the nitrogen is derived from native soil nitrogen. Treatment studies demonstrated that the nitrogen could be reduced from 20 to 3–5 mg N I⁻¹ by any one of several biological treatment processes including bacterial denitrification (filter and pond), algae growth and harvesting, and by a combination plant growth—bacterial denitrification (“symbiotic”) process. Cost estimates for the processes studied ranged from $10 to $36 1000⁻¹ m³ (1969 dollars). Laboratory algal assays demonstrated that the nitrogen removal systems studied effectively reduced the drainage waters biostimulatory content.     

Enhanced nutrient removal by biological treatment systems

The importance of nitrogen and phosphorus in stimulating eutrophic conditions in receiving waters has been well documented. As a result, over the last decade an increased emphasis has been placed on limiting these elements in wastewater effluents. In the future, new discharge permits will include limits on both of these elements.

In 1985 a research program was initiated to conduct a pilot plant study of an anoxic/anaerobic/aerobic treatment train using primary effluent. The facility was operated at varying flow and Qr/Q ratios, and at effective mixed liquor suspended solids (MLSS) concentrations of 3100 mg/L. The results of the first 13 month operational phase indicated that the effluent concentrations of total BOD₅, TSS and nitrate nitrogen were less than 5 mg/L. Ammonia nitrogen was less than 0.2 mg/L. The solids settleability was excellent, and foaming due to Norcadia, was effectively controlled. The average overall phosphorus removal was 48%. Influent BOD₅ concentrations of less than 100 mg/L significantly reduced the system's ability to remove phosphorus. A strong relationship between the amount of carbon source in the influent, phosphorus release in the anoxic and anaerobic tanks and phosphorus uptake in the aeration basin was established.