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.     

Enrichment of a K-strategist microbial population able to biodegrade p-nitrophenol in a sequencing batch reactor

The biological treatment of a high-strength p-nitrophenol (PNP) wastewater in an aerobic Sequencing Batch Reactor (SBR) has been studied. A specific operational strategy was applied with the main aim of developing a K-strategist PNP-degrading activated sludge. The enrichment of a K-strategist microbial population was performed using a non-acclimated biomass coming from a municipal WWTP as inoculum, and following a feeding strategy in which the PNP-degrading biomass was under endogenous conditions during more than 50% of the aerobic reaction phase. Hundred per cent of PNP removal was achieved in the whole operating period with a maximum specific PNP loading rate of 0.26 g PNP g⁻¹ VSS d⁻¹. A kinetic characterization of the obtained PNP-degrading population was carried out using respirometry assays in specifically designed batch tests. With the experimental data obtained a kinetic model including substrate inhibition has been used to describe the time-course of the PNP concentration and specific oxygen uptake rate (SOUR), simultaneously. The kinetic parameters obtained through optimization, validated with an additional respirometric test, were k_max = 1.02 mg PNP mg⁻¹ COD d⁻¹, K_s = 1.6 mg PNP L⁻¹ and K_i = 54 mg PNP L⁻¹. The values obtained for the K_s and k_max are lower than those reported in the literature for mixed populations, meaning that the biomass is a K-strategist type, and therefore demonstrating the success of the operational strategy imposed to obtain such a K-strategist population. Moreover, our measured K_i value is higher than those reported by most of the bibliographic references; therefore the acclimated activated sludge used in this work was evidently more adapted to PNP inhibition than the other reported cultures.     

Influence of accumulation capacity of activated sludge microorganisms on kinetics of glucose removal

The kinetics of COD removal in nonproliferating glucose-acclimated activated sludge systems was studied. A general differential equation describing this process involves a rate constant for COD removal due to storing processes (zero order), a rate constant for COD removal due to accumulation processes (first order), and an apparent volumetric accumulation capacity. In their dependence on values of these constants, the courses of COD removal can be linear, nonlinear or combined.The rate constant of accumulation capacity (AC) saturation was found to be independent on the initial concentration of biomass and dependent on the type of cultivation or on the composition of a mixed culture. It varied from 1.8 to 2.6 h⁻¹ with activated sludge cultivated semicontinuously (nonfilamentous) and from 0.8 to 1.0 h⁻¹ with activated sludge cultivated continuously in a completely mixed unit (highly filamentous).It was found that activated sludge microorganisms cultivated semicontinuously possessed an apparent specific AC as high as 600–750 mg g⁻¹, whereas those cultivated continuously in a completely mixed unit had their AC_s totally saturated. After a 6-h period of aeration (regeneration) without the presence of an exogenous substrate, the latter microorganisms possessed an apparent specific AC of 174 mg g⁻¹.     

Diffusivity, tortuosity and pore structure of activated sludge

This paper describes new techniques in studying and defining pore morphology of activated sludge. Diffusion measurements on activated sludge are carried out in a diffusion cell. The average diffusivity in activated sludge is found to be 7.4 × 10⁻¹⁰ m² s⁻¹. Surface area determinations are used to calculate the mean pore radius of activated sludge flocs. This value is found to be between 108 and 130 Å. The tortuosity of the pores in activated sludge is also calculated and found to have an average value of 2.73.     

Biological regeneration of powdered activated carbon added to activated sludge units

Powdered activated carbon equilibrium concentrations of 0, 50, 300 and 1000 mg l⁻¹ were studies in plug-flow activated sludge units maintained at sludge ages of 3, 5, 10 and 15 days. It was noted that the percentage removal of the effluent organic matter with respect to that of a control unit increased with increasing carbon equilibrium concentration. At a given activated carbon equilibrium concentration the COD removal tended to be independent of sludge age. Freundlich isotherms showed that the apparent adsorptive capacity gradually increased with increasing solids retention time, possibly caused by partial biological regeneration of the carbon. The regeneration is determined by the ratio of biological solids to carbon solids. A preliminary model was formulated to describe the relation between the daily regenerated adsorptive capacity and influent organic matter concentration.     

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.     

Control of activated sludge filamentous bulking—III. Effect of sludge loading

Previous experiments have indicated a possibility of controlling the filamentous bulking of activated sludge by cultivating a mixed culture in a system with the plug flow pattern or in a system with a selector. These experiments, however, were conducted at approximately constant sludge load [0·3–0·4 kg BOD₅(kg MLVSS day)⁻¹] and sludge age (4·5–5·0 days) so that the results obtained had only a limited validity. Further experiments were, therefore, carried out in order to find if the previous findings hold also for activated sludge systems with high sludge loads and low sludge ages.The experiments were conducted on four activated sludge systems with different flow patterns: two of them as complete-mixing reactors and the other two as reactors with the plug flow pattern, having dispersion numbers of 0·08 and 0·07. A mixture of starch and peptone was used as the substrate. All systems were operated at sludge ages 2 and 3 days and at sludge loads from 0·5 to 2·3 kg BOD₅(kg MLVSS day)⁻¹.It was found that at sludge loads above 0·5 kg kg⁻¹ day⁻¹ mixed cultures developed in the systems with the plug flow pattern possessed high values of the SVI and contained high portions of filamentous microorganisms. This was found in spite of sufficiently high concentration gradients of the substrate along these systems. It means that plug flow and, consequently, the concentration gradient of the substrate along the activated sludge system may not be the only factor in controlling the selection of microorganisms in a mixed culture. An additional factor must exert an influence on the population dynamics and selection of microorganisms in mixed cultures at high sludge loads and low sludge ages.The experiments have confirmed findings of others that values of the SVI depend on the sludge load. However, different trends of dependence were observed in the systems with different flow patterns. While in the complete-mixing systems the SVI decreased with increasing sludge loading in the systems with the plug flow pattern it increased.A greater phosphorus demand was observed in plug flow systems than in those with complete mixing.     

The effect of water hardness on nitrilotriacetate removal and microbial acclimation in activated sludge

The effect of water hardness on microbial acclimation to the removal of nitrilotriacetate (NTA) in the wastewater treatment process was examined in 4 laboratory-scale activated sludge reactors. Consistent high removal (i.e. >90%) was observed in all 4 reactors after acclimation occurred. Removals of greater than 60% of added NTA after 8 days and greater than 90% after 15 days were observed in a continuously fed, hard water (250 mg l⁻¹ as CaCO₃) reactor. In soft water (50 mg l⁻¹ as CaCO₃) comparable removals were observed after 20 and 28 days respectively. In 24 h, semi-continuous activated sludge reactors (24 h, fill-and-draw type) removal was greater in hard water than in soft water initially, but was greater than 95% in both hard and soft water after 4 weeks.The proportion of bacteria in the activated sludge with the ability to utilize NTA increased approx. 100-fold during the acclimation period. This proportion increased faster in hard water than in soft water and faster in semi-continuous activated sludge reactors than continuous activated sludge reactors.Ultimate biodegradation of ¹⁴C[U]NTA was greater than 85% in both hard and soft water acclimated units. Accumulation of ¹⁴C in the sludge solids was negligible (<1%).     

Using the sewerage system main conduits for biological treatment. Greater Tel-Aviv as a conceptual model

The long-sought idea of using main sewerage conduits as a step-fed plug-flow reactor, where biological sludge is introduced at the head of the main pipelines (hence loop system) and where aeration is provided at various points along the loop, was investigated in this paper in both a bench-scale physical model and using the Greater Tel-Aviv (Dan Region) sewerage with design population of 1.3 million and flow of 300,000 m³ day⁻¹, as a conceptual model.Due to the inherent advantages of a step-fed plug-flow reactor where high substrate concentrations are maintained along most of the length of the reactor, (except for the final section which provides effluent polishing), the viability of the biomass is 3–5.2-fold higher than the one usually encountered in a conventional activated sludge plant, thus substantially increasing its rate and efficiency of organic substrate removal.It has been shown that in the case of Greater Tel-Aviv, replacing the activated sludge conventional treatment plant with the loop system (with only secondary clarifiers to provide the return biological sludge), or alternatively resorting to the loop system instead of doubling an existing overloaded treatment plant, will produce final efluents well below the requirements of 25 mg l⁻¹ BOD₅ and will provide savings of more than 50% in construction costs. An additional advantage of corrosion control along the main conduits thus increasing their longevity is also discussed.     

Biological treatability of dairy wastewaters

Biological treatability of an integrated dairy plant wastewater containing a small fraction of whey-washwaters mixture has been experimentally investigated. Emphasis has been placed on the assessment of the initially inert fraction, S₁ and soluble residual microbial products, S_p. Parallel batch experiments have been conducted to determine the kinetic and stoichiometric coefficients of the degradable COD. The results have shown that the wastewater tested had practically no initially inert fraction, but generated residual microbial products amounting to 6–7% of the initial degradable COD. The results obtained have been fed into a set of equations describing the steady state operation of an activated sludge system with sludge recycle and a relationship indicating the variation of the total effluent COD with the sludge age has been defined for the wastewater tested. It is noted that effluent COD cannot be biologically reduced below 85 mg l⁻¹, regardless of the sludge age, due to generation of residual fractions.     

A method for determining specific surface area of activated sludge by dye adsorption

A new technique is discussed for measuring the surface area of activated sludge. The method is shown to be easy to perform and reproduceable. The results indicate that activated sludge is highly porous with a specific surface area of between 40–140 m² g⁻¹ dry solids.     

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.     

Biodegradation of 3,4,4′-trichlorocarbanilide, TCC, in sewage and activated sludge

As part of the studies to elucidate the environmental consequences from bacteriostat usage the extent of biodegradation of 3,4,4′-trichlorocarbanilide, TCC^®, in sewage systems was examined. TCC samples uniformly labeled in either the p-chloroaniline ring (¹⁴C PCA TCC) or the dichloroaniline ring (¹⁴C DCA-TCC) were monitored in activated sludge systems by measurements of ¹⁴CO₂ evolution. As was expected, the p-chloroaniline (PCA) ring of TCC was more rapidly degraded than the dichloroaniline (DCA) ring. In a continuous flow activated sludge system (10 h retention time, 200 μg1⁻¹ TCC) acclimation to primary biodegradation was readily gained. ¹⁴CO₂ evolution from ¹⁴C PCA TCC was consistent with complete metabolism of the PCA ring while that from ¹⁴C-PCA-TCC indicated about 50% biodegradation of the DCA ring. Analysis of effluents from continuous flow activated sludge units established that TCC undergoes primary biodegradation to its chloroaniline components which are in turn biodegraded.     

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.     

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 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.     

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.     

Activated sludge response to emulsified lipid loading

The possible adverse effects of natural fats and oils (lipids) upon biological wastewater treatment systems have been the subject of much speculation and some disagreement. This study addressed the specific question of possible effects of emulsified lipids upon activated sludge process performance. Lipid form and fatty acid composition were determined on wastewater samples. Experimental studies employing bench scale activated sludge units indicated that effluent quality is either not significantly different or occasionally is better than that from sucrose supplemented control plants receiving comparable organic loading (F/M > 0.80). Furthermore, emulsified lipids clearly do not exhibit an inhibitory effect on either the specific soluble substrate utilization rate or the mixed liquor oxygen consumption rate.However, effluent quality parameters were found to be dependent upon unit lipid loading to a highly significant degree. As well, unit lipid loading (g lipid g⁻¹ MLSS-day) provided a better explanation of effluent quality than either the food to microorganism ratio or the mixed liquor lipid burden (g lipid extracted from MLSS g⁻¹ MLSS). The findings of this study indicate the conditions where lipid overloading occurs. This data provides a basis for controlling emulsified lipid loading to the activated sludge process which should apply to plants which receive high lipid loading such as those encountered in industrial wastewater treatment applications.     

The performance of activated sludge plants compared with the results of various bacterial toxicity tests—A study with 3,5-dichlorphenol

It was investigated whether and to what extent the results obtained by various methods of determining bacterial toxicity in waste water could be applied to conditions prevailing in activated sludge plants or in receiving water.3.5-Dichlorphenol (DCP) was studied as an example of a persistent chemical which constitutes a pollution risk to water. The bacterial toxicity limits determined by five different methods—respiration after a 20-h consumption period, consumption rate after 2-h incubation, dehydrogenase activity determined with TTC. gas formation in a fermentation tube and inhibition of the cell division of Pseudomonas—all agreed with the toxicity limit of 5 mg DCP I⁻¹ found in degradation tests in laboratory activated sludge equipment. No safety margin need be taken into account when the test results are applied to biological purification plants.In the activated sludge plants the degradation of the industrial waste water was markedly impaired only when the DCP concentration was increased to 25 mg I⁻¹. This varied in degree according to the sludge load at the beginning of the trial.Shock loads of DCP did not cause the expected fall-off in degradation but only a moderate fluctuation in its rate. The decline in degradation following continuous and also discontinuous addition of DCP was largely or completely overcome within a few weeks by the bacteria becoming adapted to DCP.In samples of river water the toxicity limit as determined by the tests was in the region of 2 mg I⁻¹.     

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.