Removal of organic acids by activated sludges

Removal of coexisted volatile organic acids was studied using three kinds of activated sludges; treated with sewage, digested night soil and undiluted night soil at the plant scale and laboratrial experiment. Concentration of volatile fatty acids in sewage were too low to be detected, meanwhile 5–28 ppm of acetic acid were detected in influent of aeration tank of digested night soil treatment plant, and 1335–5340 ppm of acetic acid were detected in night soil. Removal rates of acetic acid were 35.9 mg g⁻¹ h⁻¹ by sewage activated sludge, 33.6 mg g⁻¹ h⁻¹ by digested night soil activated sludge and 16.9 mg g⁻¹ h⁻¹ by undiluted night soil activated sludge under coexisting volatile fatty acids. This difference depends on the number of bacteria in the activated sludge. Dissimilation percentage of acetic, propionic, butyric and valeric acids were similar results in these activated sludges.     

Adaptation of methanogenic sludge to high ammonia-nitrogen concentrations

The influence of ammonia-nitrogen concentrations in excess of 1500 mg 1⁻¹ on the methane formation from volatile fatty acids by two types of methanogenic sludge was investigated in batch experiments. One was digested sewage sludge, acclimated to 815 mg 1⁻¹ ammonia-nitrogen and the other was digested piggery manure, acclimated to an ammonia-nitrogen concentration of 2420 mg 1⁻¹. In the experiment with digested sewage sludge, methane formation took place still at an ammonia-nitrogen concentration as high as 5 g 1⁻¹. However, an increasing lag-phase was observed at increasing ammonia-nitrogen concentrations in the range 730–4990 mg 1⁻¹. On the other hand in digested piggery manure methane formation immediately started without any lag-phase in the ammonia-nitrogen concentration range of 605–3075 mg 1⁻¹. In the experiments with both types of sludge the maximum methane formation rate slowly decreased with increasing ammonia-nitrogen concentrations.     

Bioleaching of metals from sewage sludge: Microorganisms and growth kinetics

Microbial leaching is one of the advantageous methods of removing heavy metals from sewage sludge, however, the microbiological aspects of this technology have not been studied. This study presents the characterization of the naturally occurring microorganisms, responsible for the metal leaching activity, in 21 different sewage sludges. The results obtained indicate that the bioleaching of metals is carried out by successive growth of less-acidophilic and acidophilic thiobacilli. Several species of less-acidophilic thiobacilli participate in the sludge acidification, but Thiobacillus thioparus is the most important species. In contrast, Thiobacillus thiooxidans seems to be the only species involved in the acidophilic group of thiobacilli. The growth kinetics of the two groups of thiobaciili was followed in five different sewage sludges. After 5 days of incubation in shake flasks, the pH of the sludge was decreased to about 2.0 and this pH decrease solubilized the toxic metals (Cd: 83–90%; Cr: 19–41%; Cu: 69–92%; Mn: 88–99%; Ni: 77–88%; Pb: 10–54%; Zn: 88–97%). The maximum specific growth rate (μ_max) for the less-acidophilic thiobacilli varied between 0.079 and 0.104 h⁻¹ and that for the acidophilic thiobacilli varied between 0.067 and 0.079 h⁻¹.     

Total metal concentrations and partitioning of Cd, Cr, Cu, Fe, Ni and Zn in sewage sludge

Application of the BCR three-step sequential extraction procedure to sewage sludge samples collected at an urban wastewater treatment plant (Dom ale, Slovenia) is reported. The total concentrations of Cd, Cr, Cu, Fe, Ni and Zn and their concentrations in fractions after extraction were determined by flame or electrothermal atomic absorption spectrometry (FAAS, ETAAS) under optimised measurement conditions. Total acid digestion including hydrofluoric acid (HF) treatment and aqua regia extraction were compared in order to estimate the efficiency of aqua regia extraction for determination of total metal concentrations in sewage sludge. It was found experimentally that aqua regia quantitatively leached these heavy metals from the sewage sludge and could therefore be applied in analysis of total heavy metal concentrations. The total concentrations of 856 mg kg⁻¹ Cr, 621 mg kg⁻¹ Ni and 2032 mg kg⁻¹ Zn were higher than those set by Slovenian legislation for sludge to be used in agriculture. Total concentrations of 2.78 mg kg⁻¹ Cd, 433 mg kg⁻¹ Cu and 126 mg kg⁻¹ Pb were below those permitted in the relevant legislation. CRM 146R reference material was used to follow the quality of the analytical process. The results of the BCR three-step sequential extraction procedure indicate high Ni and Zn mobility in the sludge analysed. The other heavy metals were primarily in sparingly soluble fractions and hence poorly mobile. Due to the high total Ni concentration and its high mobility the investigated sewage sludge could not be used in agriculture.     

Septage disposal in waste recycling ponds

Experiments were carried out to investigate the feasibility of septic tank sludge (septage) disposal into pilot-scale waste recycling ponds for the production of algae and fish. A septage loading of 100 kg COD ha⁻¹ day⁻¹ to four 4-m² single-stage ponds resulted in the production of algal biomass and dissolved oxygen in the pond water, suitable for Tilapia growth. Some microbiological investigations of this waste recycling scheme were undertaken using ten earth ponds (each with the dimensions of 20 × 10 × 1.3 m: length × width × depth). It was found that the densities of coliform bacteria and bacteriophages in the pond water and sediment tended to increase with increased septage loadings and loading periods. The ponds fed with septage at the loading of 100 kg COD ha⁻¹ day⁻¹ were found to contain higher densities of these microorganisms than those of the control pond without septage feeding. The possible public health impact resulting from this practice was assessed.     

The response of activated sludge to a polychlorinated biphenyl (KC-500)

A kind of polychlorinated biphenyl, Kanechlor 500, was selected as a representative industrial toxicant, and its effects on biochemical characteristics of the activated sludge and its behavior in the biological treatment process were observed at concentrations of 0, 1.5 and 10 μg l⁻¹.The presence of PCB in synthetic sewage resulted in changes in the microflora and aldolase activity of the activated sludge even at low concentration of PCB such as to be 1 μg l⁻¹, and it was also demonstrated that dosing PCB caused remarkable increase of the oxygen uptake activity. Furthermore, PCB was not found to undergo degradation to any appreciable extent during the aeration process nor as the result of anaerobic digestion, although low concentrations did not exert an influence on COD and BOD removal efficiency in the process. In synthetic sewage PCB was shown to undergo mobilization from the aqueous phase to the activated sludge as evidenced by a concentration factor on the order of 10³–10⁴.     

Nitrification kinetics in activated sludge at various temperatures and dissolved oxygen concentrations

Activated sludge from a domestic sewage works was enriched with nitrifying bacteria by running a laboratory fermenter on ammonia-supplemented sewage. This enriched culture was used to determine respirometrically the kinetics of microbial nitrification. It was demonstrated that the reaction fits the Michaelis-Menten model for temperatures from 10 to 35°C, having a temperature optimum at 15°C (K₃ 0.72 mg 1⁻¹ NH₃). Nitrification is unaffected by high dissolved oxygen concentration 38 mg 1⁻¹ O₂ at 30°C) after acclimatisation. Nitrite concentrations > 20 mg 1⁻¹ are inhibitory to the reaction.     

The application of an upflow reactor in the denitrification step of biological sewage purification

A study is made of the biological purification of sewage by the denitrification process, using an upflow reactor which does not contain any granular material for attached growth. In the experiments nitrate as such was added to the sewage. At a sludge load of about 0.18 g COD/g MLSS day, 70% purification, based on COD, was obtained. The amount of the removed COD oxidized by the nitrate was 63%. At a linear velocity through the upflow reactor of 0.12 m h⁻¹ the sludge mass concentration was about 30g SS 1⁻¹.Based on the results of the experimental work the application of an upflow reactor for denitrification in a new sewage purification system—called the two-sludge system with pre-denitrification—is discussed.     

Removal of indigenous rotaviruses during primary settling and activated-sludge treatment of raw sewage

An eight month study of indigenous rotavirus removal during primary settling and activated sludge treatment of raw sewage was made in a plant in Houston, Texas treating 1.5 million gal day⁻¹. An average reduction of 44–55% was obtained by primary settling and a 93–99% reduction was achieved in final chlorinated effluents. Composite sampling at 1 h intervals over a 24 h period indicated average removals of 85% compared to a misleading 6% indicated by one set of grab samples of raw sewage and effluent collected simultaneously. Quantification of rotaviruses was made by immunofluorescent foci counts 24 h after addition of sample concentrates to coverslip cultures of fetal rhesus kidney cells. Rotaviruses varied from 40–5101⁻¹ of raw sewage and from 0 to 25 in the final chlorinated effluent.     

The effect of pretreatments on the virus contents of sewage samples

By isolations of virus from sewage and sludge samples, which had been fractionated by centrifugation at 9000 rev min^-1, it was found that virus may be particle bound and recoverable in the precipitates. An exception was the secondary sludge of the activated sludge treatment. It was thus indicated that removal of a part of a sewage or sludge sample before examination may make true quantitative estimations impossible.Re-examination of samples after storage at −20°C for 6 months gave remarkably poor virus recoveries.     

Coliform and chemical oxygen demand removal from meatworks effluents by different treatment processes

Raw effluents from meatworks were found to have high levels of bacterial contamination, comparable to those found in domestic sewage. Counts of 4 × 10⁷ ml⁻¹ for total aerobes and 10⁷ ml⁻¹ for total coliforms were obtained. Four effluent treatment processes were examined for effectiveness of removal of bacteria, chemical oxygen demand (COD) and suspended solids (SS). Lagoon and activated sludge systems were the most efficient, followed by physico-chemical treatment and lastly by high-rate trickling filtration. Both the lagoon and activated sludge systems achieved large reductions in total coliform counts, usually by factors of between 10³ and 10⁴. The effluents from both these systems nearly met normal discharge requirements for COD and SS, but the bacteriological quality was still poor.     

Anaerobic degradation of nonionic and anionic surfactants in enrichment cultures and fixed-bed reactors

Anaerobic biodegradation and inhibitory effects of nonionic and anionic surfactants on methanogenic fermentation were tested in incubation experiments with anoxic sediment samples and sewage sludge. Alkylsulfonates and alkylbenzenesulfonates were not degraded but inhibited methanogenesis from sludge constituents at concentrations ≥10 mgl⁻¹. Sodium dodecylsulfate was at least partly degraded after adaptation at concentrations 100 mgl⁻¹ and the sulfate group was reduced to sulfide. The polyethyleneglycol moiety of alkylphenolethoxylates was fermented to methane at concentrations 500 mgl⁻¹ whereas the alkylphenol residue probably remained unchanged. Alkylethoxylates were completely degraded to methane and CO₂ at concentrations up to 1.0 gl⁻¹. Complete anaerobic degradation of this surfactant type to methane, CO₂, and traces of acetate and propionate was demonstrated in a lab scale anaerobic fixed-bed reactor, either with prereduced mineral salts medium or with air-saturated artificial wastewater. This process lends itself as a suited, inexpensive means for treatment of wastewaters containing enhanced loads of nonionic surfactants, e.g. from the surfactant manufacturing or processing industry.     

The effects of organotin on the activated sludge process

Organotin compounds which find increasing use in marine antifouling paints may be present in the discharge from dry dock operations. This investigation was aimed at determining the effect of such wastewater when discharged to a municipal activated sludge treatment plant. Experiments were conducted using a Warburg respirometer and continuous flow bench-scale activated sludge systems. The results showed that unacclimated biological cultures can be inhibited by tributyl tin oxide (TBTO^™) concentrations as low as 25 μgl⁻¹. However, TBTO doses of over 8000 μgl⁻¹ can be tolerated by a well acclimated culture. Continuous loading of up to 1000 μgl⁻¹ TBTO had no effect on organic removal in activated sludge systems. However, an adverse effect on sludge settleability was noticed at 100 μgl⁻¹ TBTO. Shock loadings of 500 and 1000 μgl⁻¹ TBTO had no effect on soluble organic removal but resulted in impaired settling and higher effluent suspended solids. The LC₅₀ of TBTO to the fathead minnow was estimated at 45–200 μgl⁻¹. The toxicity was reduced considerably by activated sludge treatment.     

Direct analytical procedure for determination of volatile organic acids in raw municipal wastewater

A direct analytical method for identification and determination of the individual volatile acids in raw sewage was developed. The proposed procedure is rapid, omitting tedious sample pretreatment and thus avoiding possible losses involved in steam distillation, evaporation or extraction. It consists of direct injection of raw sewage into a gas chromatograph, including Carbowax 20 M on acid washed Chromosorb W column and a flame ionization detector. Sample preparation is confined to addition of solid metaphosphoric acid to the raw sewage, and removal of precipitated proteins and suspended solids by centrifugation.The direct injection method proved to be practicable, accurate and rapid. Volatile acids content in raw municipal sewage in Haifa, Israel, was found to be in the range of 150–160 mg l⁻¹, of which 120–125 mg l⁻¹ was acetic acid, 30–33 mg l⁻¹ propionic acid, 6–8 mg l⁻¹ butyric acid, 2 mg l⁻¹ isovaleric acid, and 0.5–1 mg l⁻¹ valeric acid.     

Variation of sludge volume index with activated sludge characteristics

Activated sludge samples from 2 laboratory units and 12 sewage treatment plants were examined to determine the effect of filamentous microorganisms, floc size and suspended solids concentration on SVI. An attempt was also made to correlate SVI to zone settling velocity. At a suspended solids concentration range of 700–4800 mg 1⁻¹ there was no effect of filamentous microorganisms at filament length concentrations below 10⁷μm (mg SS)⁻¹. However, when it was over 10⁷ μm (mg SS)⁻¹ SVI increased sharply with increasing concentrations of filamentous microorganisms.At all suspended solids concentrations examined SVI varied with floc size at filament length concentrations below 10 μm (mg SS)⁻¹. But, at filament length concentrations higher than this level, no effect of floc size on SVI was observed.The effect of suspended solids concentration on SVI was examined at different levels of filament lengths. It was found that the shape of SVI-suspended solids concentration curve varied with the level of filament lengths. A well defined relationship was found between SVI and zone settling velocity at all suspended solids concentrations examined.     

The behaviour of nitrilotriacetic acid during the anaerobic digestion of co-settled sewage sludge

The removal of nitrilotriacetic acid (NTA) in four laboratory scale anaerobic digesters treating mixed primary sludge has been investigated. Two digesters received mixed primary sludge containing 30% waste activated sludge whilst the remaining two received 15% waste activated sludge. Nitrilotriacetic acid was added at concentrations between 10 and 30 mg l⁻¹. Digesters which received waste activated sludge previously aerobically acclimatised to NTA removed NTA after periods of adaptation between 4 and 16 days.A memory effect was observed over periods of up to 30 days. It was concluded that the mechanism of NTA removal was biological. The type of organism responsible for NTA removal, and the possible impact of NTA on sludge treatment, sludge disposal and the receiving environment is discussed.     

Anaerobic treatment of wastes containing methanol and higher alcohols

Experiments have been performed to ascertain the feasibility of anaerobic digestion for the treatment of an alcoholic waste (i.e. fusel oil), consisting of approx. 50% methanol and 50% higher alcohols. Batch experiments as well as continuous experiments have been conducted. The continuous experiments have been carried out using the “Upflow Anaerobic Sludge Blanket” (UASB-) process. As inoculum a sugar beet waste grown and highly settleable and active anaerobic sludge (SBA-sludge) has been used. The SBA-sludge was shown to be superior to digested sewage sludge as seed material for an anaerobic treatment process, because—although it in fact is adapted to the fermentation of volatile fatty acids (VFA)—it does not have any significant difficulty with respect to the methanogenesis of the alcohols present in the fusel oil waste. The breakdown of higher alcohols starts immediately and that of methanol within a few days, depending on the initial load applied. In the UASB-experiments sludge loads up to 0.6 kg COD·kg VSS⁻¹·day⁻¹ could already be well accommodated within 1 week, so that within this period a space load could be handled as high as 20 kg COD·m⁻³·day⁻¹, simply by supplying the reactor with approx. 30 kg SBA-VSS·m⁻³ averaged over the total reactor volume.Contrary to recent findings of Smith & Mah (Appl. envir. Microbial. 36, 870–879, 1978), which were obtained with a pure culture of Methanosarcina barkeri, the sludge is capable of fermenting VFA and methanol rapidly and simultaneously, provided the conditions for VFA and methanol fermentation are favourable. However, as in previous experiments with aqueous solutions of methanol (Lettinga et al., Water Res. 13, 725–737, 1979), we observed that the digestion process can easily become upset, especially with respect to the degradation of VFA. Once again indications have been obtained that one or more trace elements are of eminent importance with respect to the stability of the process. At present the operation of a stable anaerobic treatment process for methanolic wastes cannot be guaranteed.     

Effect of copper on nitrification in activated sludge

The concentration of free copper in activated sludge with copper added is strongly influenced by pH. For example, at pH 6.5 with 9.13 × 10⁻⁵ mol Cu l⁻¹, the free copper concentration is 4.0 × 10⁻⁷ mol l⁻¹ (pCu = 6.4) and at pH 8.4 this concentration is 10⁻⁸ mol l⁻¹ (pCu = 8.0). In both cases the activated sludge concentration is 0.7 g MLSS l⁻¹. The free copper concentration is also affected by the concentration of mixed liquor suspended solids (MLSS).In batch experiments with constant pH, the effect of copper on the nitrification rate was not regulated by total copper concentration but by copper/sludge ratio or by free copper concentrations. Experiments at different pH showed a linear correlation between nitrification capacity and free copper concentration, suggesting that the pH effect on nitrification below 8.3 is in fact a copper effect.Activated sludge with copper did not become acclimatized to the copper in a period of three days. Addition of nitrilotriacetic acid (NTA) within one day did cancel the copper inhibition.The results were compared with the effect of copper on acetate removal by heterotrophic micro-organisms. The nitrifiers proved to be no more susceptible to copper than heterotrophic micro-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.     

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.