Palm oil refinery wastes treatment

Effluent from the refining of crude palm oil was subjected to physical-chemical and biological treatment. An inclined corrugated parallel plates oil separator spaced at 25 mm was used with hydraulic loading rates of 0.2, 0.5 and 1 m³ m⁻²-h. 91% oil and grease removal could be achieved at 0.2 m³ m⁻²-h. Coagulation and flocculation carried out on batch samples after oil and grease separation revealed that with 100 mg l⁻¹ alum addition BOD was reduced from 3500 to 450 mg l⁻¹ and COD from 8600 to 750 mg l⁻¹ after 30 min settling. Higher doses of alum and doses of polyelectrolyte, activated carbon and sodium hypochloride did not yield significant additional reductions in BOD and COD. Batch dissolved air flotation (DAF) removed 90% of the suspended solids with 2.7% solids in the thickened sludge at an A/S ratio of 0.014. This method yielded the similar effluent quality as the inclined corrugated plates oil and grease separator. Field data from a DAF plant compare closely with data achieved in this study. Activated sludge treatment on the effluent from the oil separator yielded a BOD of 46 mg l⁻¹ with a loading rate of 0.3 g BOD (g MLVSS)⁻¹-day. Total dissolved solids (TDS) remained high and removal through coagulation and chemical oxidation brought the COD level down to around 180 mg l⁻¹. Biokinetic coefficients Y, k_dK and K₃ were found to be 0.85 g VSS (g BOD)⁻¹, 0.016 day⁻¹, 0.12 g BOD (g VSS)⁻¹-day and 510 mg l⁻¹ BOD respectively.     

A comprehensive study on the biological treatabilities of phenol and methanol—I. Analysis of bacterial growth and substrate removal kinetics by a statistical method

An unbiassed statistical method was developed to evaluate kinetic parameters in the biological oxidation of wastewaters. Through the statistical analyses of the biological oxidation kinetics, it was shown that the kinetic equations satisfactorily described the bacterial growth and substrate removal kinetics where X is biomass concentration, S is substrate concentration, t is time, a is cell yield coefficient, k_d is cell decay coefficient, K_s is Michaelis-Menten constant, and k is substrate removal rate coefficient. The coefficients K_s and a changed with temperature insignificantly while k and k_d were closely related to it. The temperature independent coefficients K_s and a were estimated to be 236 mg 1⁻¹ (standard deviation, σ = 70 mg 1⁻¹) and 1.21 (σ = 0.06) respectively for phenol, and 2330 mg 1⁻¹ (σ = 1410 mg 1⁻¹) and 1.25 (σ = 0.45) respectively for methanol based on total organic carbon (TOC) and volatile suspended solids (VSS). The oxygen utilization rate can be formulated as where Rr is the oxygen utilization rate (mg 1⁻¹ O₂ time⁻¹), as′ is a coefficient designating oxygen requirement per substrate utilized, and b′ is a coefficient designating oxygen requirement per biomass for endogeneous respiration. The coefficient a′ was 1.39 for phenol and 2.23 for methanol, and b′ was 1.42 k_d for both substances based on TOC and VSS.     

Pentachlorophenol biodegradation—I: Aerobic

The biodegradation of pentachlorophenol (PCP) was tested in a three phase protocol. Phase I involved acclimation; phase II allowed determintion of biodegradation kinetics through use of continuous stirred tank reactors (CSTR) operated at solids retention times of 3.2, 7.8, 12.8 and 18.3 days; phase III assessed the importance of volatilization and sorption in PCP removal and evaluated the extent of biodegradation. Over the range of SRT's studied, PCP was found to be biodegradable with first order kinetics; the rate constant (μ_m/K_s) had a value of 0.0017 l μg⁻¹d⁻¹. The minimum concentration of PCP attainable in a CSTR was found to be 27 μg l⁻¹. Additional studies suggested that the full relationship between the PCP degradation rate and the PCP concentration followed an inhibition-type function, with the maximum rate occurring at a PCP concentration of around 350 μg l⁻¹. Radioisotopic studies revealed that PCP was mineralized by the culture, with the liberation of CO₂ and the incorporation of carbon into cell material. Neither volatilization nor sorption removed significant amounts of PCP from the reactors.     

Hypolimnetic aeration: field test of the empirical sizing method

A hypolimnetic aeration system was recently installed in a small (16 ha S_α) eutrophic lake and a comparison made between measured performance and predicted performance from an empirical sizing method. The design variables used to size the system were: hypolimnetic volume 451,600 m³; maximum hypolimnetic oxygen consumption 0.2 mg l⁻¹ d⁻¹; aerator input rate 2 mg l⁻¹; water velocity 0.76 m s⁻¹ and depth of air release 12.2 m. A 3.7 kW compressor (0.57 m³ min⁻¹) generated a water velocity of 0.46 m s⁻¹, a water flow of 17.7 m³ min⁻¹ and a theoretical hypolimnetic circulation period of 18 days. Dissolved oxygen increased by an average of 1.6 mg l⁻¹ on each cycle through the aerator, and aerator input rates ranged from 0.6 to 2.6 mg l⁻¹. Hypolimnetic oxygen consumption averaged 0.12 mg l⁻¹ d⁻¹ and ranged between 0.02 and 0.21 mg l⁻¹ d⁻¹. The aeration system was unable to meet the daily oxygen demand (90 kg) as the water velocity was slower than expected (0.46 m s⁻¹). To avoid undersizing future aeration installations the following recommendations should be considered when using the empirical sizing formula: (1) estimates of oxygen consumption should be annual maximums from aerobic hypolimnia; (2) aerator input rates should be conservative (e.g. 1–4 mg l⁻¹) and increase with depth; (3) water velocity of 0.45–0.50 m s⁻¹ should initially be used when no information on actual bubble size or velocity is available; (4) aeration start-up should be timed to avoid periods of accumulated oxygen demands.     

Aerobic stabilization of primary and mixed primary-chemical (alum) sludge

This study was conducted to investigate the feasibility of using aerobic digestion as a method for the stabilization of mixed primary-chemical (alum) sludge from a physical-chemical treatment plant. Aerobic digestion was carried out in “continuous” flow (batch fed once a day) laboratory reactors with detention times ranging from 5 to 35 days held at 7, 12, 18 and 25°C.Temperature was found to have a slightly greater influence on the reduction of volatile suspended solids in primary sludge than in mixed primary-chemical sludge. Nitrification took place in the reactors treating both primary and mixed primary-chemical sludge. The high content of aluminum in the mixed primary-chemical sludge did not inhibit the nitrifiers. The oxygen-uptake rate varied between approximately 5 mg O₂ g⁻¹ VSS h⁻¹ and 1 mg O₂ g⁻¹ VSS h⁻¹ depending on the detention time and the reactor temperature. Adenosine triphosphate content per unit volatile suspended solids indicated a low content of active biomass during aerobic digestion.     

Études des transformations des formes du carbone, azote, phosphore, soufre et des principaux éléments minéraux au cours de la mesure de la demande totale en oxygene—III transformation des formes du soufre

Previous experiments carried out with the laboratory TOD meter Ionics 225 of the DOW Chèmical made it possible (after a high temperature catalytic action) to characterize the stable forms of organic and inorganic carbon and nitrogen (NH₄⁺, NO₂⁻, NO₃⁻), and the principal cations (Na⁺, K⁺, Ca²⁺, Mg²⁺) in the course of the total oxygen demand (TOD) measurement.The object of this study is firstly to compare the oxidation capability of different techniques of organic pollution (particularly the COD and TOD) in relation to the constituent elements of the organic matter C, N, P, S, and to calculate the possible interferences of the inorganic compounds at the time of TOD test.These investigations warrant the application of this technique to measure the amount of organic pollution in relatively mineralized conditions (Industrial wastewater, sea-water…). The present publication is concerned more with the study of the transformation of the organic and inorganic sulphur forms (S²⁻, SO₃²⁻. SO₄²⁻) in the course of the TOD measurement.The study of the oxidizability of the organic sulphur compound type C_xH_yO_zS, made it possible to establish a specific relation with a ratio of 0–50 mg of organic sulphur l⁻¹, between the oxygen demand of this element [TOD (S)] and its concentration (TOD (S) = 0.97 [S]).These tests showed a partial oxidation of the sulphur to SO₂ and SO₃ as the literature claimed. On the other hand, the oxidation of the same compounds during the COD tests varies greatly and although it is not possible to establish a correlation between these two measurements, as applies in the case of organic nitrogen, nevertheless these experiments showed a greater reliability of the TOD compared with the COD in the oxidation of organic matter in general. We then carried out experiments on the different mineral forms of sulphur in order to distinguish the possible effects and to recommend simple improvements.A relative study on sulphate ions had been carried out with standard solutions which have the same TOD (the basic TOD is obtained using potassium phthalate acid) and the same increasing concentration of the salt M₂SO₄ type. The experiments showed that the basic TOD decreases when the concentration of sulphate ions is increased (Fig. 3). Therefore, the interference is negative and taking into consideration the specific oxygen demand of the cation, we can propose an evaluation of this interference (ΔTOD (SO₄²⁻) = 0.203 [SO₄²⁻]). The same experiments have been conducted with a salt of M₂SO₃ type and similar results obtained (Fig. 5).The specific interference of the sulphite ion is negative and can be estimated by the following equation (ΔTOD (SO₃²⁻) = 0.132 [SO₃²⁻]). In both cases, we have to note that the transformation of these inorganic anions occurs between those relative to the theoretical dissociation reaction corresponding to the appearance of the oxide SO₂ and SO₃. For sulphurous on the contrary, the interference is positive and therefore corresponds to an extra oxygen demand (Fig. 8).The experiments were conducted directly with the M₂S salts (M representing K or Na) in aqueous solution.The evaluation of this interference had been made in the consideration of two concentration ranges of the sulphurous ions (0–35 mg S²⁻ l⁻¹): TOD (S²⁻) = 0.4 [S²⁻] and (35–100 mg S²⁻ l⁻¹): TOD (S²⁻) = 1.2 [S²⁻] − 30.Therefore this study confirms a better oxidation of the organic matter by TOD test in comparison with COD test.But sulphate and sulfite have a negative interference in the TOD measurement, whereas sulphurous is positive.The evaluation model of these interferences allows a correction to be made of the TOD value or to verify TOD measurement of organic pollution obtained by this technique.     

Thermophilic anaerobic digestion of palm oil mill effluent

A laboratory study was carried out using the thermophilic anaerobic process to treat palm oil mill effluent containing 67,000 mg 1⁻¹, COD, 31,800 mg 1⁻¹ suspended solids and a pH of 4.5. Completely mixed reactors were operated to evaluate the effects of feed strength and solids retention times on the system's performance. A range of 5–35 days solids retention time was studied. COD reduction was 72% for the 5-day unit and greater than 90% for units having detention time 15 days or more. pH of all units was self adjusted to 7.4. Gas production was, in general, greater than 0.3 m³ kg⁻¹ volatile solids feed.     

Restoration of heavily polluted branches of the Shatt Al-Arab river, Iraq

In view of the desire to improve the water quality of the heavily polluted branches of the Shatt al-Arab River at the City of Basrah, it was proposed to maintain effective flushing as well as contracting sewerage system. The present study was conducted in order to examine the water quality of these branches in an attempt to evaluate the effectiveness of the proposed flushing system. It has been found that their waters contained very low levels of dissolved oxygen and relatively high amounts of both COD and BOD₅. The annual average water quality parameters for Basrah Branches were: dissolved oxygen 3.4 ppm; pH 7.67; hydrogen sulphide 1.4 ppm; ammonia 97 μg-at. N l⁻¹; COD 15.9 mg l⁻¹; BOD₅ 12.7 mg l⁻¹; dissolved silicates 202 μg-at. Si l⁻¹; dissolved reactive phosphate 13.4 μg-at. P-PO₄³⁻ l⁻¹; nitrate 10.4 μg-at. N-NO₃⁻ l⁻¹; nitrite 2.1 μg-at. N-NO₂⁻ l⁻¹ and chlorophyll-α 14.3 mg m⁻³. Based on our calculations, it has been concluded that the proposed system is effective, thus within a flushing cycle all of the above mentioned parameters will become within the acceptable values of the Shatt al-Arab water quality. Moreover, this system has no appreciable effect upon the water quality characteristics of the Shatt al-Arab River due to the fact that it discharges a high volume of water annually. However, It has been recommended to dredge the deposited sludge to a minimum depth of 50 cm.     

Anaerobic filter treatment of molasses distillery slops

Anaerobic filter treatment of beet molasses distillery slops was carried out in laboratory and pilot scale reactors. During a one year operation period volumetric loadings of up to 50 kg VS m⁻³ d⁻¹, corresponding to a hydraulic residence time of approx. 1 day, were achieved. The biogas yield was between 430 and 460 l kg VS⁻¹ resulting in a gas productivity of between 13 and 20, 5 m³ m⁻³ d⁻¹.     

Influence of high NaCl and NH4Cl salt levels on methanogenic associations

The effect of high levels of NaCl and NH₄Cl on the activity and attachment of methanogenic associations in semi-continuous flow-through reactor systems has been evaluated. Two well-functioning reactors received shock concentrations of NaCl and NH₄Cl while two other reactors were adapted to increasing levels of the salts during a period of 45 days. The methanogenic associations, grown on a medium containing mainly acetate and ethanol, were found to be more resistant to NaCl and NH₄Cl than previously reported. Initial inhibition occurred at shock treatments of 30 gl⁻¹ for both salts. The reactors which were gradually exposed to increasing levels of the salts, adapted well and their tolerance levels surpassed those of the non-trained counterparts. Initial inhibition and fifty percent inhibition was observed at 65 and 95 gl⁻¹ respectively for adaptation to NaCl. Initial inhibition for the reactor adapting to NH₄Cl occurred at 30 gl⁻¹ and a 50% inhibition was observed at 45 gl⁻¹ of NH₄Cl. For the reactors receiving NH₄Cl, the free ammonia-N should be kept below a concentration of 80–100 mg l⁻¹ for optimal performance. The bacterial populations in the reactors consisted mostly out of Methanosarcina (> 99% of the biomass)     

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.     

The behaviour of phosphate, nitrate, chloride and hardness in twelve welsh rivers

Selected water quality data from 12 rivers in the area administered by the Welsh Water Authority were analysed for the period 1974–1981. Mean nitrate-nitrogen concentrations varied from 0.4 to 3.7 mg l⁻¹ and were significantly related to the intensity of average catchment run-off; mean orthophosphate-phosphorus concentrations ranged from the limit of analytical detection to 0.730 mg l⁻²; chloride from 11 to 42 mg l⁻¹ and total hardness (as CaCO₃) from 13 to 173 mg l⁻¹. Seasonal patterns of change in concentration were established, generally for all determinands at most sites, but no long-term trends were detected. Relationships between concentration and flow were established for most determinands at many sites, increasing flow generally resulting in decreased concentration. However, positive relationships between nitrate concentration and flow were established at seven sites. Mass flows (kg ha⁻¹ yr⁻¹) were calculated at nine sites only: nitrate-N 4.8–24.6; orthophosphate-P 0.16–3.81; chloride 79–334; total hardness (as CaCO₃) 196–1629. Orthophosphate flows were related to sewered population density, estimates of per capita and land drainage contributions being 1.9 g day⁻¹ and 0.112 kg ha⁻¹ yr⁻¹ respectively.     

A comprehensive study on the biological treatabilities of phenol and methanol—III Treatment system design

The effects of temperature, pH, salinity, and nutrients on bacterial activities were investigated and evaluated using a statistical method. The substrate utilization rate coefficient (k) decreased as pH deviated from neutral and as salinity increased, and the unfavorable pH and salinity alleviated the temperature effect on k. The modified Arrhenius equation, k_T2 = k_T1 θ(^T2−T1), was not effective in describing the temperature effect on k: the temperature coefficient (θ) ranged between 1.0–1.4 depending on the temperature range, pH, salinity, and substance (phenol or methanol). The endogeneous respiration activity was affected by various environmental factors such as pH, temperature, and salinity; however, the cell decay coefficient (k_d) turned out to be correlated to a single parameter, k. Thus, k_d = 0.066 k^0.87 and k_d = 0.0115 k^0.634, where k and k_d are based on the unit of h⁻¹, were proposed for the prediction of cell decay coefficient for phenol and methanol acclimated activated sludge, respectively. In batch treatment of 770 mg l⁻¹ of phenol and 1000 mg l⁻¹ of methanol as TOC, nitrogen and phosphorus did not have any recognizable effect on k, while trace elements such as Fe²⁺, Mg²⁺, Mn²⁺, Ca²⁺, and Zn²⁺, etc. showed a slightly perceptible effect on it. The absence of extra-cellular nitrogen and phosphorus resulted in a greater cell yield; however, the cells in this condition decayed more rapidly than normal cells. The primary factor affecting the substrate decomposition rate in natural systems was pH: phenol decomposition resulted in a considerable decrease in pH so that the buffering capacity of the water was the most important factor, and methanol decomposition did not affect pH significantly so that the initial pH of the water was the most important factor. An initial lag phase was observed in 8 out of 115 phenol batch tests and 31 out of 66 methanol batch tests.     

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.     

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.     

Stability and performance of anaerobic fixed film reactors during hydraulic overloading at 10–35°C

Anaerobic fixed film reactors could be hydraulically loaded to 94 kg COD m⁻³ day⁻¹ for a 24 h period and regain normal performance 12–48 h after overloading. COD conversion decreased with increased overloading and was dependent on operating temperature and type of waste. The quality and amount of digester gas was also affected but returned to normal steady values once overloading was stopped.     

Removal of organics from leachates by anaerobic filter

A laboratory-scale study was conducted on two anaerobic filters at several loading rates and four hydraulic detention times. Feed substrates were landfill leachates taken from a recently opened landfill (Keele Valley) and from an older site (Brock North) which had been closed for about 8 years. The strong raw leachate from the new landfill had a COD of 14,000 mg l⁻¹, a BOD/COD ratio of 0.7 and a COD/P value of 17,900. The partially stabilized leachate from the older landfill had a COD of only 3750 mg l⁻¹, a BOD/COD ratio of 0.3 and a COD/P value of 30,640.Results from the treatment of the two leachates were compared with those from a previous study of a “mature” landfill (Beare Road). It was demonstrated that the anaerobic filter could reduce the COD of leachate from landfills of different ages by 90%, at loading rates of 1.26–1.45 kg COD m⁻³ d⁻¹. Total biogas production ranged between 400 and 500 l gas kg⁻¹ COD destroyed and methane content between 75 and 85%. No phosphorus addition was required over the loading range studied.     

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).     

Growth kinetics of the filamentous microorganism Sphaerotilus natans in a model system of a food industry wastewater

Bulking by Sphaerotilus natans has been attributed to several factors such as low dissolved oxygen in the aeration basin, wastes with high C:N ratios and phosphorus limitation; however, the occurrence of bulking has been reported in fruit, vegetable, meat and poultry wastewaters in which the ratio C:N is variable.Growth of S. natans was analyzed in a model system of a food industry wastewater (potato processing waste) that was characterized by HPLC determining that citric acid was the most important identified component. The effect of several carbon sources on S. natans growth was also studied; different C:N ratios were tested in a continuous culture system (chemostat). This strain grew in a mineral medium with citric acid as a sole carbon source, in spite of the contradictory results found in literature. Chemostat studies showed that the medium was carbon-limited when C:N ratios <19 mgCOD (mgN-NH₃)⁻¹. Monod kinetic growth coefficients, determined for this strain in chemostat were: maximum specific growth rate, μ_max=0.301 h⁻¹; Monod constant, K_S=4.6 mgCOD l⁻¹; true biomass growth yield, Y^T_X/S=0.490 mgVSS (mgCOD)⁻¹; endogenous decay rate, k_d=0.011 h⁻¹ and maintenance coefficient, m_S=0.022 mgCOD (mgVSS)⁻¹ h⁻¹. The obtained parameters were compared with literature data and the effect of glucose and citric acid as carbon sources was discussed; these parameters are useful in modeling the growth of S. natans in potato processing wastewaters (or in other effluents under carbon-limiting conditions) especially when citrate is the main component and can be used to control filamentous bulking by metabolic or kinetic selection.     

Silage effluent digestion by an upflow anaerobic filter

Silage effluent is generally regarded as one of the major agricultural pollutants of water courses. Efficient anaerobic digestion of silage effluent was achieved by a 3-day hydraulic retention in an upflow anaerobic filter. The filter was a laboratory scale unit containing a limestone chip support matrix. At loading rates ranging from 7.8 to 14.2 kg COD m⁻³ active volume day⁻¹, the average COD removal obtained ranged from 86 to 89% with a TOA removal of 82–88%. The methane content of the biogas produced ranged from 81 to 88%. The rate of COD conversion to CH₄ was independent of the loading rate under the conditions tested and the observed efficiency averaged 0.357 m¹ CH₄(STP) kg⁻¹ COD introduced to the reactor.The reactor tolerated considerable variation in influent pH without any apparent decrease in digestion efficiency. It is apparent from the results obtained that a reactor which is in routine use for slurry digestion may also be utilised for silage effluent digestion on a seasonal basis.