High nitrate denitrification in continuous flow-stirred reactors

Continuous flow stirred reactors were used to evaluate the maximum denitrification specific removal rates for influent solutions made from NH₄NO₃, CaNO₃, KNO₃ and UO₂ fuel fabrication waste water. Nitrate substrate concentrations ranged from 0.01 to 20 kg NO₃/m³. Values for U_max (maximum specific substrate removal rate per unit mass of microorganisms per unit time, days⁻¹) were determined using graphical solutions to the Lineweaver-Burk equations. For NH₄NO₃ solutions at nitrate substrate concentrations <6 kg NO₃/m³ the value for U_max was found to be 1.73 days⁻¹. At nitrate substrate concentrations >6 kg NO₃/m³ a nonlinear relationship was observed in the Lineweaver-Burk plots indicating nitrate substrate inhibition. Specific removal rates at nitrate concentrations >6 kg NO₃/m³ averaged <1.0 days⁻¹. Ammonia toxicity may also have occurred as the pH of the mixed liquor was near 8. Methanol concentrations as high as 11.6 kg CH₃OH/m³ did not inhibit denitrification rates. The highest specific removal rates recorded (3.13 ± 0.56 days⁻¹) were with influents made from UO₂ fuel fabrication waste water.     

Nitrate reduction by denitrifying bacteria in single and two stage continuous flow reactors

Denitrification by a mixed bacterial population of medium containing 1000 mg NO₃⁻-N1⁻¹ and acetate as carbon source was studied in batch, a single stage continuous flow stirred reactor (CFSTR) and a two stage CFSTR at 30°C. The optimum pH for denitrification, nitratase, nitrite reductase activities and growth was found to be 7.5 in batch culture. A single stage CFSTR growth limited by nitrate had an optimum denitrification rate of 0.13 mg NO₃⁻-N mg⁻¹ cells h at a residence time of 8 h. The experimentally observed carbon to nitrate ratio (mg CH₃ COO⁻-C mg⁻¹ NO₃⁻-N)was 1.7 for the dilution rates of 0.02–0.18 h⁻¹. For the second stage CFSTR, bacteria growing at the maximum rate of 0.25 h⁻¹ and not limited by nitrate had a denitrification rate of 0.24 mg NO₃⁻-N mg⁻¹ h. Dissolved oxygen (up to 9.5 mg 1⁻¹) did not effect denitrification rates in the second stage CFSTR. As the second stage CFSTR runs progressed extensive wall growth occurred and concurrently the output gas contained increasing quantities of nitrous oxide. A development from this study would be a two stage CFSTR with wall growth in the second stage which would make an efficient nitrate removal process.     

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.     

Detoxification of seawater used for gas scrubbing in the steel industry

Cyanide ion present in seawater after scrubbing blast furnace and coke ovens gases can be removed by sedimentation of hexacyanoferrate complexes followed by oxidation of residual cyanide with Caro's acid. Zinc ion is removed at the same time by adsorption on the hexacyanoferrate/hydrous ferric oxide precipitate.Sulphide is precipitated as ferrous sulphide, then oxidised by atmospheric oxygen. At 25°C and using an Fe/CN ratio of 1·00, initial concentrations of 50 mg l⁻¹ of CN⁻ and 10 mg l⁻¹ of Zn²⁺ in seawater are reduced to 5–7 mg l⁻¹ and 0·1 mg l⁻¹. Subsequent treatment with H₂SO₅/CN = 1·2 reduces the [CN⁻] to 0·1 mg l⁻¹.Treatment of a combined blast furnace/coke ovens effluent ([CN⁻] = 24 mgl⁻¹, [Zn²⁺] = 4·0 mgl⁻¹) with Fe/CN = 1·5 reduced [CN⁻] to 0·2 mg l⁻¹ and [Zn²⁺] to <0·1 mgl⁻¹. Subsequent treatment with H₂SO₅/CN = 2·0 reduced [CN⁻] to 0·2 mg l⁻¹. The process operates best in the pH range 7–9 and so is not affected by the buffer characteristics of seawater.     

Gas production in aquatic sediments in the presence and absence of nitrate

In the overlying water of a water-sediment system the pH was controlled at 7.0, the nitrate-nitrogen concentration at 25.0 mg 1⁻¹ and the dissolved oxygen concentration above 6.1 mg t⁻¹. The temperature of the whole system was kept at 15°C. The average rate of nitrate removal from the system as a result of denitrification amounted to 160 mg NO₃⁻ -N m⁻² day⁻¹. By means of Eh measurements at various depths in the sediment, it was attempted to figure out the course of the penetration fronts of nitrate and oxygen in the sediment during 241 days of incubation. From these results the layer in which denitrification occurred was derived. The course of the denitrification zone was followed during the incubation period. As a result of the depletion of the available hydrogen donors in the sediment, oxygen reached the bottom of the sediment after 235 days of incubation.     

Removal of nitrate from effluent following discharge on surface water

The loss of nitrate nitrogen over a 800-m long reach of canal was studied in a field experiment during a 20-days period. The nitrate originated mainly from sewage effluent. Fifty-six percent of the nitrate had disappeared during its flow through the 800-m long reach, where the average retention time was 1.7 days. The average rate of nitrate disappearance during the 20-day period was 913 mg NO₃⁻-N m⁻² day⁻¹. Laboratory experiments with undisturbed water-sediment profiles from the canal showed that the disappearance of nitrate was caused mainly by denitrification in the sediment. Increased knowledge of this phenomenon may lead to an effective and cheap means in inducing denitrification.     

A modified version of the sodium salicylate method for analysis of wastewater nitrates

The German sodium salicylate method for nitrate determination has been modified and improved by utilizing flocculating effect of the preservative HgCl₂ (1000 mg 1⁻¹). The method gives highly reproducible results in the range of 0·2–16 mg 1⁻¹ nitrate nitrogen and is applicable for routine analysis of untreated sewage. Interfering substances are chloride ions above 1500 mg 1⁻¹ and nitrite ions above 10 mg 1⁻¹N. The yellow color produced by sodium salicylate with nitrate ions obeys Beer's law and remains stable for several hours.     

Responses of Cyperus involucratus Rottb. to nitrogen and phosphorus, with reference to wastewater reclamation

There is increasing use of aquatic plants in biosystems to ameliorate wastewaters. Cyperus involucratus Rottb. is a large emergent aquatic plant which may be useful in treating wastewater because it grows quickly, does not die back in winter, has little weed potential and grows in dryland situations. Many wastewaters contain high levels of N and P, and the capacity of C. involucratus to take up these nutrients was studied under glasshouse conditions. Maximum growth was attained between 84 and 168 mg NO₃-Nl⁻¹ and 1–5 mg PO₄-Pl⁻¹. At a low level of supplied NO₃-N, most of the N in plant organs was reduced-N; at levels of supplied NO₃-N above 84 mg l⁻¹, there was considerable accumulation of NO₃-N in plant organs. The accumulation of NO₃-N was greatest in culms where it made up over 50% of their N content when plants were grown on 350 mg NO₃-Nl⁻¹. Linear regression equations best described the relationships between dry matter and reduced-N contents in roots, culms and leaves. Over 60% of the total plant N and P accumulated in above ground organs, and concentrations of up to 0.53% P and 3.4% N (dry wt basis) were recorded in leaves. C. involucratus would be a suitable plant for wastewater reclamation on account of its high dry matter production, its ability to tolerate hyper-eutrophic levels of N and P, and the accumulation of most of the N and P in the harvestable portions of the plant.     

Factors affecting the denitrification rate in two water-sediment systems

Effects of temperature, oxygen and nitrate concentrations of the overlying water, and the thickness of the sediment layer on the rate of denitrification in the sediment were investigated in two water-sediment systems, A and B. At 4°C, denitrification started after a prolonged lag period in contrast to nitrification which did not occur significantly. At 15°C, and particularly at 25°C, both processes proceeded readily. The disappearance of NO₂⁻ - N from the overlying water was more rapidly than that of NO₃⁻ - N.The denitrification rate was slightly reduced by increasing the dissolved oxygen concentration in the overlying water from 0 to approximately 2 mgl⁻¹. A further rise of the dissolved oxygen concentration had no further decreasing effect on the denitrification rate.The denitrification rate in sediment was dependent on the nitrate concentration in the overlying water approximating first order kinetics at lower concentrations, gradually becoming independent of the nitrate concentration at higher nitrate contents (zero order kinetics).When starting with a nitrate-nitrogen concentration of 25.2 mgl⁻¹, a sediment layer of 7 mm with A and 14 mm with B was roughly found to be involved in denitrification.Denitrification rates found in the present laboratory experiments were supposed to be considerably lower than those occurring under natural conditions as additional mechanisms for the transport of nitrate into sediments occurred in natural environments.     

Modified curcumin and dianthrimide methods for the determination of boron in the presence of high levels of nitrate and organics

Modifications have been made to the curcumin and 1,1′-dianthrimide methods for boron analysis so that they may be used in the presence of up to 700 mg l⁻¹NO⁻₃ and 500 mg l⁻¹ organic carbon. In the curcumin method, nitrate is removed by alkaline reduction using a slurry of aluminum powder. In the dianthrimide method, nitrate up to 1000 mg l⁻¹NO⁻₃ is removed in the dehydration-with-sulfuric-acid step; organics are most conveniently removed by treatment of the dehydrated sample with solid potassium persulfate. With dianthrimide, an automated procedure is used for the colour formation and measurement steps.     

Inter-relationships between nitrogen balance, pH and dissolved oxygen in an oxidation ditch treating farm animal waste

The pathways of N in aerobic farm waste treatment systems are discussed in relation to the dissolved oxygen (DO) and pH of the mixed liquor. The change in pH, DO, oxygen uptake rate and nitrogen balance were monitored under steady, and non-steady, state conditions in an oxidation ditch treating undiluted pig waste. A kinetic analysis of the mass balance for nitrogen allowed an interpretation of the fate of nitrogen under different prevailing conditions. Undesirable accumulations of nitrite were noted in the presence of high levels of free NH₃ and HNO₂. The process was self-promoting and was encouraged by the influx of raw waste. Concentrations of 500 mg 1⁻¹ NO₂-N and 1200 mg 1⁻¹ NO₃-N were the maximum values observed and were considered to be the concentrations at which product inhibition arrested nitrifying activity. Attainment of these levels prevented complete nitrification despite an adequate retention time. pH and DO were inversely related probably through nitrification, but pH appeared to be lowered by accumulation of nitrite and nitrate anions, and thus by the balance between nitrification and denitrification. Considerable N loss through denitrification was found to occur despite apparently aerobic mixed liquors. At low DO simultaneous nitrification-denitrification could eliminate 90 per cent of the soluble-N. NH₃ desorption in laboratory cultures was found to be first order in free NH₃ but was not a significant mode of N loss under field conditions.     

Batch metal removal by peat. Kinetics and thermodynamics

Peat moss, a natural inexpensive material, is able to play an important rôle in treatment processes of metal-bearing industrial effluents since it adsorbs, complexes or exchanges various metal cations. This paper presents kinetics and thermodynamics of batch metal removal reactions by 50 g l⁻¹ (dry wt) eutrophic or oligotrophic peat particles using Cu²⁺, Cd²⁺, Zn²⁺ and Ni²⁺ concentrations ranging from 0.01 to 100 mM.Metal cation removal reactions are moderately rapid in 10 mM metal unbuffered solutions: the forward kinetic constant ranges between 0.005 and 0.17 M⁻¹s⁻¹, and equilibrium is reached within about 1 h. Under these conditions of pH (2.2–4.2) and concentrations, apparent binding equilibrium constants were found to range between 2 and 3150 M⁻¹ depending upon the peat origin and the metal cation.In 0–6.5 pH-buffered metal cation solutions, the four cations binding reactions behaved differently demonstrating that metal binding equilibrium constant decrease in the order Ni²⁺ > Cu²⁺ > Cd²⁺ = Zn²⁺. When pH is higher than 6.7, more than 90% of a 10 mM metal cation solution is removed by 50 g 1⁻¹ peat particles and metal binding capacities equal 200 mmol kg⁻¹ dry wt, whatever the metal nature and the peat origin. Except for nickel cation which is very strongly bound to peat, all metal cations are completely released when pH is fixed below 1.5.     

Nitrate determination in fresh and some estuarine waters by ultraviolet light absorption: A new proposed method

The new proposed u.v./resin technique for nitrate determination is either not affected by, or can allow for, the following interfering chemicals at levels occurring in natural polluted or unpolluted waters; chloride, phosphate, sulphate, carbonate/bicarbonate, bromide, nitrite, coloured metal complexes, humic acids, ammonium, dyes, detergents, phenol and other u.v. absorbing organics. The method is quick and has an accuracy of ±3%. Concentrations of NO₃.N in the range 0.1–3.0 mg l⁻¹ can be determined in fresh water. Concentration of the sample to determine lower levels by evaporation is feasible with certain upland waters but should not be attempted if the sample has a high humic acid concentration. The technique can only be used in nitrate rich estuarine and coastal waters because the lower limit of detection is raised to 0.5 mg l⁻¹ when the sample is diluted to remove bromide interference.     

A comparison of nutrient sources and behaviour in two lowland subcatchments of the River Wye

Seasonal changes in concentrations and mass flow of dissolved silicon, orthophosphate and inorganic nitrogen were studied during 1978 in two lowland catchments of the R. Wye, the Frome and the Trothy, which are of similar drainage area but are subjected to different land use. In addition more intensive investigation of water quality changes were undertaken during storm events.Seasonal patterns of silicon concentrations were similar in the two rivers with major depletions in May and annual losses to diatoms were estimated to be equivalent to 5–12% of annual mass flow. Peak concentrations of orthophosphate were generally recorded during periods of low river flow in both rivers but concentrations were substantially greater in the Frome (mean, 0.42 mg l⁻¹) than the Trothy (mean, 0.19 mg l⁻¹), reflecting differences in population density. The principal form of inorganic nitrogen in both catchments was nitrate, but mean concentrations were considerably greater in the Frome (mean NO₃-N. 4.99 mg l⁻¹) than in the Trothy (mean NO₃-N. 2.93 mg l⁻¹) and seasonal variations were markedly different. Concentrations in the Frome increased during the summer months (maximum, 7 mg l⁻¹ whilst concentrations in the Trothy decreased during this period and this was reflected in positive and negative relationships between concentration and river flow respectively. Such differences in behaviour cannot be attributed to contributions from sewage and it is suggested that they may reflect differences in the proportion of groundwater contributing to river flow during the summer period and the nitrate content of that groundwater.Intensive sampling during storm events indicated that, overall, orthophosphate concentrations decreased and silicon and nitrate concentrations increased with increased flow, but there was considerable variation in solute behaviour during different events.     

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.     

A simple method for the rapid determination of iron in natural waters

A simple and versatile method is described for the rapid determination of iron in natural waters using the chromogen Ferrozine. The method is capable of analysing samples with concentrations from less than 5 mg m⁻³ to 3 g m⁻³ routinely, with high precision. While the method was intended for the determination of total soluble iron, the distinction between ferrous and ferric iron is also possible.     

Effect of nitrate concentration in lake water on phosphate release from the sediment

Thirty-one Danish eutrophic lakes were investigated routinely over 1 year during the period 1978–1980. Nine lakes were dimictic with anoxic hypolimnia and 22 were very productive and shallow, polymictic lakes. Phosphate release from the sediment resulted in large increases in phosphate concentrations in anoxic hypolimnion, if concentrations of oxidized nitrogen in hypolimnion were less than about 0.1 g N m⁻³. If concentration of oxidized nitrogen (mainly nitrate) in hypolimnion was about 1 g N m⁻³ or higher, no release of phosphate from the sediment to anoxic hypolimnion occurred. In lakes with no summer stratification a release of phosphate from the sediment to the well oxygenated water resulted in summer maxima of phosphate in the lake water, when nitrate concentration in the water was less than about 0.5 g N m⁻³, but no release took place if nitrate concentration exceeded about 0.5 g N m⁻³. This effect of oxidized nitrogen in preventing phosphate release from the sediment demonstrates the ability of oxidized nitrogen to buffer the redox potential of the surface sediment at a level high enough to prevent a release of phosphate. Thus, among the efforts to limited phytoplankton biomass in lakes an artificial enrichment with nitrate may in some cases be an important supplement to the usually necessary reduction in phosphorus loading, but the possibility of a stimulation of phytoplankton growth through the addition of nitrate must be carefully considered.     

Analysis of long-term and seasonal river water quality changes in Latvia

An analysis of long-term historical records of the concentrations of major ions, TDS and nutrients for 20 river sites in Latvia is reported. Periods of water quality observations ranged from 15 to 43 years. A study of the quarterly adjusted time series showed that characteristic features of the data are non-normal distributions, seasonality, serial correlation and presence of significant trends that are mostly positive. The application of state-of-the-art software, based on non-parametric statistics such as the Seasonal Kendall slope estimator and the Seasonal Hodges-Lehmann estimator, made it possible to investigate these water quality records more accurately than other methods allow.Typical seasonal variations and concentration-discharge relationships were analyzed for different constituents. It was shown that fertilizer application and marsh land reclamation can cause widespread and intensive river water quality changes. Concentration increases of as much as 5–10 times that of background values were detected for NO₃⁻, Cl⁻, Na⁺ + K⁺ and SO₄²⁻. The main water quality changes took place in the 1960s and the early 1970s when fertilizer applications and reclamation works increased. After that, concentration increases for constituents other than NO₃⁻ and SO₄²⁻ were statistically insignficiant. The significant increases for NO₃⁻ and SO₄²⁻ were probably due to the additional impact of increased atmospheric deposition. The results of long-term changes of river loads entering the Baltic Sea and the Gulf of Riga from Latvian territory are examined.     

Heavy metal accumulation by aquatic fungi and reduction in viability of Gammarus pulex fed Cd contaminated mycelium

The addition of Pb²⁺ (1.0 and 2.5 μg ml⁻¹) and Cd²⁺ (2.5 and 5.0 μg ml⁻¹) to growth medium decreased the growth of aquatic fungi, while Zn²⁺ even at a concentration of 10 μg ml⁻¹ had no inhibitory effect. Low concentrations of Cd²⁺ and Zn²⁺ on the other hand stimulated mycelial growth. The fungi accumulated considerable amounts of metal from the growth medium, generally in the order Zn²⁺ > Pb²⁺ > Cd²⁺ · Cd²⁺ was also accumulated by fungi from successive changes of medium containing low concentrations of the metal. Application of Langmuir and Freundlich isotherms to the results showed that the metals were accumulated largely by adsorption to the surface of the mycelium.Three species of aquatic fungi supported the growth of the freshwater shrimp. Gammarus pulex when provided as sole food source, sustaining from 30 to 60% of shrimps fed for a period of 21 days. A marked reduction in shrimp viability occurred however, when G. pulex was fed Pythium sp. containing Cd²⁺ (150–170 μg g⁻¹), with none of the shrimps surviving beyond 13 days, compared with a survival rate of 60% after 21 days for shrimps fed uncontaminated mycelium. Bodies of poisoned shrimps sampled on day 13 were found to contain Cd²⁺ (22.03 μg g⁻¹) showing that the metal can be transferred from aquatic fungi to G. pulex, the first step in a food chain involving freshwater fish and higher organisms.     

The use of an upflow fixed bed reactor for treatment of a primary settled domestic sewage

This study presents and demonstrates results obtained from an half full-scale upflow fixed bed reactor (UFBR) treating a primary settled domestic sewage. This study used expanded clay with an effective size of 2.7 mm containing hematite and magnetite as a granular medium.The content of TSS in the effluent treated was always between 10 and 20 mg l⁻¹ for bed depths ranging from 2 to 3 m and filtration rates of 3–6 m³m⁻²h⁻¹.The profiles taken all along the reactor show that the activity of the biomass is constant over the whole height of the reactor. Moreover, an air/water volume ratio of 2:1 is amply sufficient to satisfy the oxygen demand of the biomass. The average removal efficiency based on the soluble COD remains virtually unchanged as a function of the filtration rate at about 70% of the influent. For a final BOD₅ of 30 mg l⁻¹, loadings of 4.5–8 kg BOD₅m⁻³ can be applied. This corresponds to filtration rates of 3–6 m³m⁻²h⁻¹. The removal efficiencies for BOD₅ are then about 80%.After optimization of the backwashing conditions, the consumption of backwash water is about 5% of the volume of filtered water.Sludge measurements carried out during our experiments indicate an excess sludge production of 1 kg kg⁻¹ BOD₅ eliminated. The nature of these sludges is very similar to the biological sludges produced in the high rate activated sludge process.This study has made it possible to establish design parameters of an UFBR and to develop technology for applications. These results are applied to two wastewater treatment plants which began to operate in 1984: these plants serve population equivalents of 40,000 and 11,000.