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.     

Denitrification with a bacterial disc unit

An enclosed rotating disc unit was operated anaerobically as a denitrifying system, with methanol as the hydrogen donor. As the bacterial population became established, denitrification rate increased by 1·5 mg NO₃⁻—N reduced m⁻² h⁻², to a maximum rate of 260 mg NO₃⁻—N reduced m⁻²h⁻¹. The C:N ratio necessary for complete denitrification was found to be 2·6:1. Optimum pH for denitrification lay in the range between pH 7·0 and 8·5. Q₁₀ values were 1·38 between 10 and 30°C, −2·66 above 30°C and 13·06 below 10°C.     

Azolla–Anabaena's behaviour in urban wastewater and artificial media – Influence of combined nitrogen

The results of using the nitrogen fixing symbiotic system Azolla–Anabaena to improve the quality of treated urban wastewater, particularly on what concerns phosphorus removal efficiencies (40–65%), obtained in continuous assays performed during the past few years and presented earlier, were very promising. Nevertheless, the presence of combined nitrogen in some wastewaters can compromise the treatment efficiency. The main goal of this work was to compare plants behaviour in wastewater and in mineral media with and without added nitrogen.Azolla filiculoides's specific growth rates in wastewater and in mineral media without added nitrogen or with low nitrate concentration were very similar (0.122 d⁻¹–0.126 d⁻¹), but decreased in the presence of ammonium (0.100 d⁻¹). The orthophosphate removal rate coefficients were similar in all the growth media (0.210 d⁻¹–0.232 d⁻¹), but ammonium removal rate coefficient in wastewater was higher (0.117 d⁻¹) than in mineral medium using that source of nitrogen (0.077 d⁻¹).The ammonium present in wastewater, despite its high concentration (34 mg N L⁻¹), didn't seem to inhibit growth and nitrogen fixation, however, in mineral media, ammonium (40 mg N L⁻¹) was found to induce, respectively, 18% and 46% of inhibition.     

Effect of operation conditions on biological Fe oxidation with rotating biological contactors

Oxidation of ferrous iron (Fe²⁺) by acidophilic iron-oxidizing bacteria was conducted with a laboratory-scale rotating biological contactor (RBC) in order to investigate the effects of Fe²⁺ concentration, pH, temperature and rotation rate. Fe²⁺ oxidation rate on RBC was expressed as a first-order reaction with respect to Fe²⁺ concentration when it was below 150 mg 1⁻¹. Fe²⁺ oxidation rate was not affected by pH from 1.0 to 2.6 nor by temperatures from 10 to 40°C but was accelerated by increasing peripheral disk velocity from 4.7 to 28.2 m min⁻¹.     

Growth and nutrient uptake of green alga, Scenedesmus dimorphus, under a wide range of nitrogen/phosphorus ratio—I. Experimental study

In order to elucidate the relation between algal growth and nutrients such as nitrogen and phosphorus, a chemostat culture experiment using Scenedesmus dimorphus was performed under the conditions of T-N/T-P ratio of 2–50 mg N mg⁻¹ P and dilution rate of 1–4 day⁻¹. It was ensured from the results that nitrogen and/or phosphorus is the limiting nutrient for the growth of this alga under these conditions. The optimum T-N/T-P ratio for its growth was observed to change from 20 to 5 mg N mg⁻¹ P as the dilution rate varied from 1 to 4 day⁻¹ and, in most of the range of T-N/T-P ratio and dilution rate, its growth rate was not regulated by only one of the available nitrogen and phosphorus concentrations in the medium and algal nitrogen and phosphorus contents. Based on these facts, the multiplicative effect rather than the threshold effect of these two nutrients on its growth was considered to exist. It has been suggested, however, that algal nitrogen and phosphorus contents, especially nitrogen content, are the most important factors regulating its growth. Nitrogen uptake rate of this alga increased at a given concentration of available nitrogen in the medium as T-N/T-P ratio decreased down to 2 or 5 mg N mg⁻¹ P. It is also suggested that a multiplicative effect of nitrogen and phosphorus on uptake of these nutrients by S. dimorphus may exist.     

The synthesis of the dissimilatory nitrate reductase under aerobic conditions in a number of denitrifying bacteria, isolated from activated sludge and drinking water

A number of denitrifying bacteria were isolated from activated sludge and drinking water. These bacteria were tested for the synthesis of the dissimilatory nitrate reductase under aerobic conditions (dissolved oxygen concentration above 4 mg · l⁻¹). The synthesis of this enzyme varied from total repression by oxygen in some bacteria, especially those isolated from drinking water, until a nearly non oxygen-repressed synthesis in other bacteria (strains 15 and N4). The effect of the dissolved oxygen concentration during growth of the bacteria on the synthesis of the dissimilatory nitrate reductase in cells of strain 15 was studied more extensively. A considerable repression of the enzyme synthesis was obtained when the dissolved oxygen concentration was relatively high (approx 15 mg·l⁻¹). Addition of chlorate to the growth medium of strain 15 (using NH⁺₄-N as nitrogen source) also resulted in a serious repression of the nitrate reductase synthesis during aerobic growth (dissolved oxygen above 4 mg·l⁻¹). The dissimilatory nitrate reductase of aerobically grown cells of strains 15 and N4 was found to be mainly localized in the membrane fraction.     

Thickening of waste activated sludge by biological flotation

Waste activated sludge was thickened by biological flotation without polymer flocculant dosage. The BIOFLOT® process utilizes the denitrifying ability of activated sludge bacteria. Gaseous products of anaerobic nitrate reduction cause spontaneous flotation of the sludge suspended solids. Laboratory tests confirmed the dependence of sludge thickening efficiency on available nitrate concentration, flotation time and temperature. Full-scale experiments were performed in a fully automatized unit for discontinuous sludge thickening from wastewater treatment plants with a capacity of up to 5000 I.E. Waste activated sludge from wastewater treatment plants at Pisek. Milevsko and Björnlunda was thickened from 6.2, 10.7 and 3.5 g/l MLSS to 59.4, 59.7 and 66.7 g/t MLSS, respectively. Concentrations of COD, ammonium and phosphate ions were decreased in sludge water. The average nitrate consumption for bioflotation was 21.2 mg NO₁⁻ per 1 g of MLSS of activated sludge. Flotation time ranged from 4 to 48 h.     

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.     

Development of mathematical models for the treatment of an industrial wastewater by means of biological rotating disc reactors

In this study the extension of the mathematical model proposed by Grieves to experimental results obtained in the treatment of an industrial wastewater is examined. The laboratory-scale unit consists of three stages with seven discs per stage.The following conclusions are drawn: (1) the Grieves's model (originally derived for glucose solutions) is reliable also for an industrial wastewater; (2) within the range of organic loading of 8.7–27.7 g BOD₅ day⁻¹ m⁻², the diffusion of the organic substrate, through the liquid film adhering to the biological film, is the controlling step of the BOD₅ removal kinetics only when the disc rotational speed n is less than 0.6 rev min⁻¹; (3) for higher values of n, as those adopted for full-scale plants, bio-disc apparatus can be designed, with good approximation, by means of the Monod's equation, by considering the bio-disc unit as an idealized perfect mixing activated sludge reactor, whose volume and activated sludge concentration are equal to the volume of the active biological film and organism concentration in the same film.     

Treatment of poultry manure wastewater using a rotating biological contactor

A pilot scale, six stage rotating biological contactor was used to evaluate the feasibility of this process for the stabilization of liquid animal manures. Total disc surface area was approx. 16.7 m². Treatment efficiencies were determined at various waste strengths and influent flow rates.With loading rates of 14.7–322 g m⁻² day⁻¹, the average COD reduction was 61%. With loading rates of 4.88-24.4 g m⁻² day⁻¹, the average BOD₅ reduction was 87%. Total nitrogen removal averaged approximately 30% for the entire study. Mixed liquor oxygen uptake rates were generally in excess of 80 mg 1⁻¹ h⁻¹.Clarified effluent was non-odorous and suitable to be reused for manure flushing or spray irrigation. Treatment was not sufficient to permit effluent discharge to surface waters.     

Isotope tracer methods for investigations of nitrogen deficiency in Castle Lake, California

Previous studies conducted at Castle Lake, California suggested that phytoplankton growth could be limited by low levels of dissolved inorganic nitrogen during the summer growing season. We have used the isotopes H¹⁴CO₃⁻, ¹³NH₄⁺, ¹⁵NO₃⁻, and ¹³NO₃⁻ as tracers to determine the rates of inorganic carbon and nitrogen uptake by the natural phytoplankton community and their response to nitrogen enrichment. Experimental designs followed the procedures of several bioassay techniques which have been developed to investigate algal nutrient deficiency.The results indicate that the phytoplankton were nitrogen deficient throughout the growing season. Ammonium uptake was rate-limited by the external concentration of ammonium. Nitrate uptake was regulated by the availability of nitrate and molybdenum, and potentially by the assimilation of ammonium. Although N-enrichment enhanced photosynthesis in short-term experiments during the early portion of the growing season, the photosynthetic response was initially negative during midseason, and a positive response did not occur until 2–3 days had elapsed. This suggests that a lack of stimulation, or even inhibition, of inorganic carbon uptake upon nitrogen enrichment does not necessarily preclude N-deficiency.     

High-rate overland flow

Recommended loading rates for treating raw domestic wastewater by overland flow are 6.3–15 cm wk⁻¹. Information provided in the literature yields little insight regarding the upper range of hydraulic loading rates that could be effectively treated by overland flow. Therefore, field investigations were conducted to evaluate the performance of the overland flow system at overland flow rates from 0.95 m³ day⁻¹ m⁻¹ width of slope (13 cm wk⁻¹ to 4.15 m³ day⁻¹ m⁻¹ (57 cm wk⁻¹).Preliminary treated municipal wastewater was pumped to overland flow slopes, each approx. 3.7 m wide and 36.5 m long. The slope of each plot was 2.5%. The cover crop consisted of a mixture of ryegrass, bluegrass and fescue grass. The plots were operated for 2 years at six different hydraulic loading rates.Effluent BOD₅ concentration averages varied from 6 to 11 mg l⁻¹. The reduction of influent BOD₅ concentration ranged from 87 to 93%. Mean effluent suspended solids values were from 6 to 9 mg l⁻¹ with reductions of influent concentrations of 91–95%. Hydraulic application rate had little effect on percent BOD₅ or suspended solids removal.Total phosphorus reductions were minimal at all hydraulic application rates due to limited soil water contact.Ammonia concentration in the effluent ranged from 1 mg l⁻¹ NH₃-N at the 0.95 m³ day⁻¹ m⁻¹ (13 cm wk⁻¹) applied flow rate of 11.7 mg l⁻¹ NH₃-N at the 4.15 m³ day⁻¹ m⁻¹ (57 cm wk⁻¹) loading rate. Ammonia and nitrogen reductions decreased as the applied flow rate increased. Consequently, lower overland flow rates are necessary for nitrogen removal.The use of high-rate overland flow could potentially reduce the land necessary for this form of land application, if nutrient removal was not a local concern.     

Treatment of low strength domestic wastewater using the anaerobic filter

A laboratory scale anaerobic filter packed with synthetic high surface area trickling filter media was used to treat a low strength domestic wastewater averaging 288 mg 1⁻¹ COD. The filter was operated for 60 days after reaching steady-state at 20, 25, 35°C at a loading rate of 0.02 lb COD ft⁻³ day⁻¹ and 24 h hydraulic retention time. Filter effluent BOD₅ averaged 38 mg 1⁻¹ providing an average removal rate of 79%, and effluent COD averaged 78 mg 1⁻¹, corresponding to a 73% removal rate. Removal efficiencies showed very little sensitivity to daily fluctuations in influent wastewater quality. The filter performance at 25 and 35°C was not significantly different, but BOD and TSS removal efficiency declined a: 20°C. Gas production averaged 0.027 ft⁻³ of gas per ft³ of influent wastewater, or 1.875 ft³ of gas per pound of influent COD. Gas composition averaged 30% nitrogen, 65% methane, and 5% carbon dioxide. Ammonia nitrogen and sulfides both increased during treatment. It is concluded that the anaerobic filter is a promising candidate for treatment of low strength wastewaters and that post treatment for sulfides and ammonia may be necessary.     

Hazards associated with the use of chlorinated oxidation pond effluents for irrigation

Eight milligrams per litre chlorine applied to oxidation pond effluents caused no algal kill within the first 2 h of contact. The available chlorine attacks bacteria causing coliform count to drop from 10⁵ 100 ml⁻¹ to a few tens. Enterovirus counts dropped from about 80 100 ml⁻¹ before chlorination to 37 100 ml⁻¹ (after chlorination). Vibrio cholerae (El-Tor) were killed under these adverse conditions, and MPN dropped from 10³ 100 ml⁻¹ in the influent wastes to 2 100 ml⁻¹ in the effluents. A 5 mg l⁻¹ dose of chlorine at 1 h contact time killed these sensitive bacteria decreasing MPN to less than 2 100 ml⁻¹.Differences between the efficiency of chlorination experiments under laboratory and field conditions would necessitate the application of 15 mg l⁻¹ chlorine for 2 h of contact.     

Low temperature removal of nitrate by bacterial denitrification

The efficiency of two denitrifying sludges enriched at 5 and 20°C were compared using methanol as an electron donor. Both sludges were exposed to the same hydraulic and chemical conditions using an influent containing methanol and mineral salts. The low temperature sludge seemed to have several advantages over the sludge selected for at the higher temperature. In the range 0–17°C, the specific denitrification rate was 1.5–4 times the rate for the high temperature sludge, temperatures below 8°C being the most favourable. At 2°C, under nitrate limiting conditions, 98% nitrate reduction was obtained at a hydraulic residence time of 3.5 h, with an effluent concentration of 0.8 mg NO₃---Nl⁻¹. Sedimentation characteristics were always better for the low temperature sludge, and the utilization of methanol equally good as the high temperature sludge. The low temperature sludge appeared to be biochemically and microbiologically stable to temperature changes within the range 0–17°C, the latter temperature being close to the limit for maintaining the psychrophilic characteristics of the sludge. Studies on pure culture isolates of the denitrifying bacteria showed >90% dominance of one bacterial strain in both sludges. Studies of the isolates also showed that the low-temperature sludge consisted predominantly of psychrotrophs/psychrophiles, and not well-adapted mesophiles, which were only present in low concentrations. The dominant strain in both sludges was unable to grow on methanol in pure culture without access to nutrient growth factors. Only a few minor strains were obligate methylotrophs.Low temperature sludges were tested in a 3-stage biological process receiving domestic sewage. Each stage; carbon oxidation, nitrification and denitrification had separate sludge recycle, and methanol was added to the denitrification stage. These sludges were grown and selected for at temperatures 5°C. At 5°C the laboratory scale process gave 90% removal of total nitrogen at hydraulic residence times of 1.5, 9 and 4 h for the two aeration stages and the anaerobic stage respectively. Overall nitrification/denitrification was 95%, while denitrification separately was 98%. The effluent contained 0.4 mg NO₃---Nl⁻¹. The critical step in the process was unquestionably nitrification. Oxidation of ammonium was satisfactory at low temperature, but the reaction was somewhat vulnerable to changes in external conditions. The low temperature denitrifying sludge was originally enriched on synthetic waste but did not appear to change its microbial composition or characteristics by exposure to municipal wastewater.     

A mercury-free accelerated method for determining the chemical oxygen demand of large numbers of water samples by autoclaving them under pressure with acid-dichromate

In order to fulfill the objective of a water control program based on frequent sampling in several wastewater treatment plants, rivers and lakes a simplified method for measuring COD was developed. The procedure, in this article called the RR-method, includes: small sample and reagent volume; rapid addition of a mixture of all reagents to the sample; exclusion of mercury; autoclaving at 120°C for 1 h in flasks with fitted glass stoppers. To avoid dilution before analysis the method has been adapted for wastewater (I: 10–300 mg O₂ l⁻¹) and fresh water (II: 10–100 mg O₂ l⁻¹).Parallel analyses on different types of water samples according to Standard Methods showed that the yield by the RR-method was about 10% lower (Table 2). With water from the wastewater treatment plant at Uppsala (COD around 20 mg O₂ l⁻¹), the two methods gave an identical result. The somewhat lower yield was mostly due to decreased dichromate concentration and oxidation temperature. The lower oxidation potential made correction for chloride interference unnecessary below 1 g Cl⁻ l⁻¹ (Table 1).The RR-method also showed a good correlation to the values for KMnO₄-consumption. Parallel analyses of 318 samples from 14 wastewater receiving lakes gave the correlation coefficient r = +0.90 (Fig. 1).     

Role of aquatic plants in wastewater treatment by artificial wetlands

This report describes investigations using artificial wetlands which quantitatively assess the role of each of three higher aquatic plant types, Scirpus validus (bulrush), Phragmites communis (common reed) and Typha latifola (cattail), in the removal of nitrogen (via sequential nitrification-denitrification), BOD and TSS from primary municipal wastewaters. During the period August 1983–December 1984, the mean ammonia concentration of 24.7 mg l⁻¹ in the primary wastewater inflow (hydraulic application rate = 4.7 cm day⁻¹) was reduced to mean effluent levels of 1.4 mg l⁻¹ for the bulrush bed, 5.3 mg l⁻¹ for the reed bed and 17.7 mg l⁻¹ for the cattail bed, as compared to a mean value of 22.1 mg l⁻¹ for the unvegetated (control) bed. For all three vegetated beds, the mean effluent ammonia values were significantly below that for the unvegetated bed and for the inflow. The bulrushes and reeds (in that order) proved to be superior at removing ammonia, both with mean effluent levels significantly below that for the cattail bed. The high ammonia-N (and total N) removal efficiencies shown by the bulrush and reed beds are attributed to the ability of these plants to translocate O₂ from the shoots to the roots. The oxidized rhizosphere so formed stimulates sequential nitrification-denitrification. Similarly BOD removal efficiencies were highest in the bulrush and reed beds, both with mean effluent BOD levels (5.3 and 22.2 mg l⁻¹, respectively) significantly below that for the unvegetated bed (36.4 mg l⁻¹) and equal to or better than secondary treatment quality (30 mg l⁻¹). Our results demonstrate that higher aquatic plants can indeed play a significant role in secondary and advanced (N removal) wastewater treatment by wetland systems, a role that is completely distinct from that associated with their pollutant uptake capacity.     

Field studies on coliphages and coliforms as indicators of airborne animal viral contamination from wastewater treatment facilities

The occurrence of animal viruses in the aerosol emissions of wastewater treatment facilities was evaluated by direct assay and by the use of coliforms and coliphages as indicator organisms. Coliforms and coliphages were compared and evaluated with regard to their suitability as indicators of airborne animal viral contamination from wastewater treatment facilities. Two plants, one with treatment by activated sludge and the other by trickling filtration, were studied. Field air sampling procedures used large-volume air samplers, with recirculation devices, and Andersen samplers. Airborne viruses were enumerated by a most probable number (MPN) procedure. Partially treated liquid sewage contained about 1.0 × 10² pfu l⁻¹ of animal viruses assayed on Buffalo Green Monkey (BGM) cells, 3.6 × 10⁵ and 5.0 × 10⁵ pfu l⁻¹ of coliphages, depending upon the E. coli host strain used for assay, and 2.0 × 10⁹ colonies l⁻¹ of coliform bacteria. No airborne animal viruses were recovered, airborne coliphage levels averaged 2.3 × 10⁻¹ and 3.0 × 10⁻¹ MPN m⁻³, coliforms from aerosol emissions were 2.1 × 10² colonies m⁻³. Ratios of coliphages to animal viruses indicate that wastewater treatment plants may be continuous sources of low level concentrations of animal virus aerosols. Evidence shows coliforms to be much less stable than coliphages in the airborne state. Coliphages may be a more acceptable indicator of airborne animal viral contamination than coliforms.     

Rising sludge in secondary settlers due to denitrification

High suspended solids concentrations in settler effluents can be caused by rising sludge, which is the effect of flotation of solids by nitrogen gas resulting from biological denitrification. Many factors influence the nitrogen gas bubble evolution. The most important factor is the rate of biological denitrification. Factors like nitrogen gas solubility and oxygen concentration in settler influent only play a minor role. The hydraulic retention time in the bottom part of the settler is, for all practical purposes, so high that sufficient nitrogen gas will be generated at temperatures above 20°C, if the nitrate content in the influent to the settler is above the critical one. For temperatures around 20°C the critical nitrate-nitrogen concentration is 6–8 g NO₃⁻-N/m³. The best measure in order to avoid rising sludge is to denitrify the wastewater in the treatment process ahead of the settler.     

Liquid/suspended solid phase partitioning of polycyclic aromatic hydrocarbons in coal coking wastewaters

Wastewater samples were collected from five streams among two coke plants and characterized by high pressure liquid chromatography and gas chromatographic mass spectrometry. Wastewater streams included the ammonia still influent, ammonia still effluent and biological oxidation effluent. Samples collected from these streams were separated into liquid and suspended solid phases and each phase was analyzed for eleven polycyclic aromatic hydrocarbons (PAH). Total wastewater concentrations for these compounds ranged from about 2000 μg l⁻¹ in the ammonia still influent to 5–120 μg l⁻¹ in the biological oxidation effluent. Wastewater PAH were partitioned between liquid and suspended solid phases, and in most samples suspended solid phase PAH accounted for approx. 80% or more of total wastewater PAH. Partitioning in the biological oxidation effluent stream was correlated with aqueous solubility and n-octanol/water partition coefficients. Wastewater treatment consisting of sedimentation, ammonia stripping, and biological oxidation generally reduced liquid phase PAH concentrations to the range of 1 μg l⁻¹ or less. Effective removal of wastewater suspended solids will reduce total effluent PAH concentrations, hence there is need to address issues regarding removal of residual wastewater suspended material including characterization of the distribution of PAH with respect to suspended particle size.