Evaluation of biomass age in activated sludge processes

The effect of chronic exposure of sublethal concentration (5%) of vegetable oil factory effluent on ovarian maturation of Channa punctatus was studied. The process of ovarian recrudescence was significantly retarded as evidenced by the low ovarian weights and low occurrence of Stage III (Yolky) oocytes in the ovaries of effluent-exposed fish. A high incidence of atresia was also noticed in the ovaries of fish exposed to the effluent.     

The speciation of metals in sewage and activated sludge effluent

A gel filtration chromatography technique was used to separate soluble species of Cd, Cu, Co, Mn, Ni, and TI in the influent and effluent of a laboratory scale activated sludge simulation operated at a range of sludge ages from 3 to 18 days. It was found that, whilst there was no general trend for all six metals, Cd and Mn associated mainly with low molecular weight fractions; Co, Cu, and Ni with a range of predominantly high molecular weight fractions; and TI tended towards association with high molecular weight fractions which influenced metal solubility and appeared to be significant in determining metal removal. It appeared that all metals exhibited high affinity for mixed liquor suspended solids (MLSS) and that this affinity was strongest for Cu and Cd. Nickel, Co, Cu, and TI appeared to show a high affinity for polymeric microbial products produced at longer sludge ages. The gel filtration technique was found to be useful in the separation of metal species in conjunction with a sufficiently sensitive detector provided their concentrations in the original sample were relatively high.     

Stoichiometric modeling of the activated sludge process

A mathematical model of the activated sludge process is solved with consideration given to the wastewater composition. Inclusion of wastewater composition will lead to predictions where N or P may be limiting nutrients. The procedure presented is useful when designing or evaluating the operation of an activated sludge process.     

The stimulation of filamentous microorganisms in activated sludge by high oxygen concentrations

A laboratory study was conducted to compare the response of an activated sludge culture proliferating in an environment where the DO concentration was maintained between 8-9 mg l^?1 to that of a culture in an environment where the DO concentration was 2 mg l^?1 when both systems were subjected to identical loading fluctuations. It was observed that in the high DO system, filamentous microorganisms became the predominate form when the suspended solids concentration dropped below a value near 4000 mg l^?1. However, no filamentous growth appeared in the alternate system until the suspended solids level dropped below 500 mg l^?1. A model is developed which proposes to explain this observation.     

Additional studies on the use of cracking catalysts in conjunction with activated sludge wastewater treating

A previous study indicated that regenerated spent fluid catalytic cracking catalyst, added to a test activated sludge system, increased the sludge settling rate, decreased the settled sludge volume (compaction), decreased the supernatant (effluent) TOC and increased the supernatant optical clarity. In addition, phosphate levels were markedly reduced in a municipal sewerage a ctivated sludge system. As an extension of this study, fresh, spent, and regenerated cracking catalysts have been examined to determine if the observed activity could be attributed to the carbon and metals deposited on the catalyst during the cracking operation. To do this the earlier studies have been repeated and adsorption isotherm tests have been conducted with fresh, spent and regenerated catalysts. The results indicate that: (1) the carbon and metals on the catalyst surface do not affect the improved settling and compaction of activated sludge observed when the catalyst is present, nor do they affect TOC removals; (2) none of the catalysts tested adsorb soluble TOC to an appreciable extent; and (3) the presence of catalyst, by enhancing compaction, may stabilize the activated sludge system during wet weather conditions.     

About the functional similarity of activated sludge and soils in the context of interdisciplinary studies and the biosphere preservation

The development of a concept of ecological functions of soils has facilitated interdisciplinary studies in various fields of soil science and neighboring sciences. As is shown in this paper, the ecological functions of activated sludge have a lot of features similar to the ecological functions of natural soils. A classification of the major ecological functions of activated sludge is suggested. It is stressed that the role of activated sludge as a protective barrier is particularly important for the biosphere preservation, as the self-purification capacity of many water objects is almost exhausted. In general, activated sludge can be considered a biological reactor of a polyfunctional character.     

Control of odors arising from the thickening of surplus activated sludge in the dissolved air flotation unit

This paper reports on investigations carried out to determine the feasibility of using various types of adsorbent medium to remove odors emitted during the thickening of surplus activated sludge by the dissolved air flotation (DAF) process. The performances of four different commercial grades of granular activated carbon and a grade of activated alumina were evaluated using a pilot facility set up at a local wastewater treatment plant. The odorous air directly above the DAF unit was pumped simultaneously through a set of columns each filled with the appropriate test adsorbent until odor breakthrough occurred. Air samples were collected at the inlet and outlet of each column and also at intermediate sampling ports located along the column. The odor concentration of air samples was assessed by dynamic olfactometry and the capacity of the various media for removing sewage odor was evaluated and compared. Results revealed that the odor concentration of the influent column air averaged 35 son m^?3. Of the four activated carbon grades tested, the alkali impregnated carbon that is frequently recommended for used at sewerage facilities was found to be least effective in the treatment of odors from the DAF unit. The capacity of the various media tested ranged from about 2650 son kg^?1 for the worst activated carbon grade to 37 510 son kg^?1 for the activated alumina which was the most cost effective adsorbent used. It is estimated that the cost for treating a given volume of odorous air at the DAF unit with activated alumina will be less than 65 % of the most economic activated carbon grade.     

Optimizing the design of an activated sludge/secondary clarifier system via univariate search technique

This article presents a simple and effective univariate search technique which is suitable for optimizing the design of an activated sludge/secondary clarifier system on microcomputers. The usefulness of the proposed optimal design procedure was tested on an IBM personal computer (IBM-PC). The results of this study indicated that the least-cost design of a typical activated sludge/secondary clarifier system can be obtained within 4 min on an IBM-PC. Besides, the proposed procedure was also found capable of obtaining the optimum solution over a wide range of initial step size of search chosen.     

The influence of transient phenomena on the biodegradation of nitrilotriacetic acid in the activated sludge process I: Variations in hydraulic loading and sewage strength

The removal of nitrilotriacetic acid (NTA) following acclimatization in an activated sludge pilot plant has been studied during transient changes in operating conditions. These changes included increases in hydraulic loading and influent chemical oxygen demand (COD) and such phenomena in combination with transient temperature reductions. Short-term increases in hydraulic loading from 1 to 2 dry weather flow (dwf) had a very limited effect on NTA removal. Increasing the influent COD had a slight effect on NTA removal. Short term increases in hydraulic loading combined with transient reductions in temperature significantly reduced NTA removal. The effect of these combined changes on NTA removal was synergistic, rather than additive. Increases in influent COD combined with transient temperature reductions also caused a significant reduction of NTA removal. The effect of such combined changes on NTA removal was at most only additive.     

The influence of transient phenomena on the biodegradation of nitrilotriacetic acid in the activated sludge process II. Variations in influent metal and NTA concentrations

A BASIC microcomputer program is described which calculates the median lethal dosage (LD₅₀), the probit transformation, 95% confidence limits and a chi-square test for goodness of fit quantal response data. The program could also be modified for use on other microcomputers, making it an extremely useful program in environmental toxicology research.     

Medically used radionuclides in sewage sludge

The concentration of medically used radionuclides has been studied in sludge from the sewage treatment plant serving the borough of Malmo. In this area all nuclear medicine procedures are carried out in one hospital and almost all patients live in the borough. Therefore, the input of medically used radionuclides into the sewage system can be estimated with good accuracy. Samples of digested sludge have been taken once or twice a week during half a year. Iodine-131 (physical half life (T) = R.05 d) was detected in all samples. The ¹³¹I-activity concentration due to medical use varied between (0.03±0.01) and (0.12±0.02) nCi kg^?1. The ratio between the total output of ¹³¹I via the sludge and an adherent input of the radionuclide into the sewage system was determined to (2.6 ± 0.6) × 10^?3, which is equivalent to a ratio of (2 ± 1) × 10^?2 for stable I. Occasionally measurable activities of ¹⁹⁸Au (T=2.7 d) and ²⁰¹T1(T=3.l d) have been found. The radioactivity concentration of medically used radionuclides in the sludge is low and constitutes no health problems for the persons involved. The sludge however has proved to be a very sensitive and suitable integrator of radioactive material released from a large urban area.     

Evaluation of crystalline components in sewage sludge

Abstract

Crystalline minerals in anaerobically digested sewage sludges were determined by x‐ray diffraction analysis. Sludge samples were prepared for x‐ray analysis by either washing with H₂O to remove soluble salts or oxidizing organic matter with H₂O. A limited number of minerals are present as crystalline materials in sludge. Even though the sludges contained appreciable concentrations of Cu, Zn, Cd, Pb and Ni, no crystalline metal sulfides, phosphates, hydroxides, oxides or carbonates were found with the exception of a possible Cu, Zn carbonate hydroxide. All other crystalline components detected are common minerals such as quartz, feldspar, montmorillonite, chlorite, mica, dolomite and calcite.     

Copper species in aqueous sewage sludge extract

The Cu in the saturation extract of dried Davis sewage sludge was mainly in a complexed form. A Cu²⁺ specific ion electrode was used to determine the extent of complexation. The adsorption coefficient for the complexed Cu on Yolo silt loam was 4 while for Cu added as CUSO₄ it was 90 L kg^?1 at relevant Cu concentrations in solution. Paper electrophoresis was used to define the Cu complexes according to their mobility in an electric field. Six fractions of positive, negative and neutral charge were isolated. The portion of Cu in the sludge which was water soluble increased significantly upon drying. The large percentage of complexed Cu and its relatively low adsorption on soil suggested that sewage sludge may, under certain conditions, be a source of Cu contamination of plant systems and, in extreme cases, of ground water.     

Affinity constants and behavior of Cd sorption in some acid soils

Cadmium sorption was studied in several acidic soils in a pH range from 4.5 to 6.5. The soils had two classes of surfaces with acidity constants (pKa₁ = 4.09 and pKa₂ = 6.39) similar to those for weakly and very weakly cidic carboxyls, and N-containing groups in fulvic acid. Titratable H and acidity constants were used to estimate the number of exchange sites at each pH level. Sorption of Cd was closely related to Cd concentration, pH, and soil type. Although the inclusion of pH and organic C contents in a regression accounted for some variations in the Cd distribution coefficient defined as the ratio of the quantity of Cd sorbed to the solution Cd concentration, the number of sorption sites was a more appropriate factor to explain the variability. Because of a negligible contribution to the number of exchange sites from Fe oxides, the sorption of Cd at pH = 4.5 was considered to be of a one-surface Langmuir type. A two-surface Langmuir equation was considered to model sorption at higher pH values. The average affinity constants (log K) were 3.61 and 4.89 for Cd sorption by the two classes of surfaces.     

The fate of metals in sewage sludge incinerators

The fate of heavy metals in multiple hearth sewage sludge incinerators was examined using mass balance techniques. All major process streams into and out of the incinerators were sampled in order to characterize the partitioning of Cu, Ni, Ph, and Cd into the major effluent streams, and to calculate a metals mass balance around the incinerators. The results indicate that the residual particulate matter from the incineration process becomes progressively more enriched in the more-volatile metals (Cd and Ph) with decreasing particulate size, in the order bottom ash < cyclone ash < scrubber water particulate < stack particulate. The less-volatile metals Cu and Ni are not similarly enriched. The mass balance indicates that approximately two-thirds of the Cd mass entering the incinerators is partitioned to the scrubber water stream, while the bottom ash stream receives most of the Cu, Ni, and Pb.     

Influence of sewage sludge from sludge beds of Ulan-Ude on the soil properties and the yield and quality of potatoes

The influence of sewage sludge from sludge beds of the city of Ulan-Ude applied to the soil separately and in combination with fertilizers (NPK) on the soil properties and the yield and quality of potatoes was studied. It was shown that sewage sludge could be used both separately (15 t/ha) and in combination with mineral fertilizers for potato growing.     

Immobilization of cadmium and zinc in soil by Al-montmorillonite and gravel sludge

We investigated the potential of montmorillonite, Al-montmorillonite and gravel sludge to immobilize polluting heavy metals in agricultural soil. Batch experiments showed that both Al-montmorillonite and montmorillonite immobilized zinc and cadmium. Zinc was bound specifically on Al-montmorillonite and became increasingly incorporated into the interlayer hydroxy-Al polymer, whereas there was no specific sorption on montmorillonite. Cadmium was bound on montmorillonite and Al-montmorillonite unspecifically by cation exchange, but there was no incorporation into the lattice. In pot experiments montmorillonite, Al-montmorillonite, or gravel sludge were added to a soil contaminated with zinc and cadmium. Increasing doses of these agents decreased the concentrations of NaNO₃-extractable zinc and cadmium. Aluminium-montmorillonite and gravel sludge were more efficient than montmorillonite in immobilizing both zinc and cadmium. Remobilization tests at pH between 4 and 5.5 showed that cadmium and zinc desorbed more easily from montmorillonite than from Al-montmorillonite. Gravel sludge application increased the buffer capacity of the contaminated soil substantially. The binding agents decreased zinc concentrations in red clover (Trifolium pratense), and gravel sludge also reduced the cadmium concentrations.     

Molybdenum hazard in land disposal of sewage sludge

The application of sewage sludge to agricultural fields may result in the production of Mo-rich herbage, a cause of metabolic disorders in animals. An alternative to application of sludge to agricultural fields is sludge utilization in strip-mine reclamation. Oxidation of strip-mine spoil material causes accumulation of Mo-rich iron oxyhydroxide in stream beds and spoil piles. Strip-mine reclamation by sludge application may induce short-term increases in the concentration of Mo and other metals in waters discharged from the reclaimed area because of pH dependent ion-exchange reactions and dissolution of Mo-bearing iron oxyhydroxides.     

Sewage sludge effects on soybean growth and nitrogen fixation

The effect of sewage sludge application, as a source of phosphorus, on dinitrogen symbiotic fixation in soybean was evaluated. The experiment was carried out in a greenhouse and included eight different treatments: (1) no fertilization, (2) complete fertilization, (3) inoculation with rhizobia plus phosphate fertilization (IS+P), (4) inoculation with rhizobia without phosphate fertilization (IS-P), (5) inoculation plus dose 1 of sewage sludge (IS+SS1), (6) inoculation plus dose 2 of sewage sludge (IS+SS2), (7) without inoculation plus dose 1 of sewage sludge, and (8) without inoculation plus dose 2 of sewage sludge. The two rates of sewage amendment corresponded to 11.2 t ha^-1 and 22.4 t ha^-1 and were calculated on the basis of the sewage phosphorus content and the amount of phosphorus recommended for soybean fertilization. Results were evaluated 49 and 63 days after plant emergence. Nodule number and weight decreased as follows: IS+P>IS+SS1, IS+SS2>IS-P. No nodules were formed without inoculation. The acetylene reduction activity was highest for the IS+P treatment 49 days after plant emergence. At the 63-day harvest that parameter was similar among IS+P, IS+SS1 and IS+SS2 treatments. The total amounts of nitrogen in shoots were similar for IS+P, IS+SS1 and IS+SS2 treatments at the first harvest but by 63 days after plant emergence, total amounts of nitrogen in above-ground parts (shoot and pods) were higher in IS+P and IS+SS2. This was due to higher pod dry weights. This study demonstrated that soybean growth can be improved by sewage sludge at a low application rate without the necessity of additional phosphorus fertilization.     

Nitrogen mineralization and nitrification in soils treated with ammonium sulfate and Nutrasweet sludge

Abstract

NutraSweet sludge, a by‐product of the manufacture of the artificial sweetener aspartame, contains about 40% of its nitrogen (N) in inorganic form and the rest mostly in the form of L‐phenylalanine. Although this sludge is often applied to land as fertilizer, the exact management strategy for its optimum use has not been clear. We conducted a laboratory study to compare the evolution of inorganic N contents and nitrification in two soils treated with NutraSweet sludge and ammonium sulfate at rates of 0, 25, 50, 100, and 150 mg N kg^‐1. Four days after application, the inorganic N recovered from the sludge ranged from 67 to 105%, indicating a fast rate of mineralization. At 25 and 50 mg N kg^‐1, the overall recovery of inorganic N from NutraSweet sludge was higher than from ammonium sulfate, whereas the converse was true at higher application rates. In Dothan soil with an initial pH of 5.5, nitrate‐N as percentage of the N applied was higher in samples with NutraSweet sludge than in those with ammonium sulfate. The opposite effect was observed in Tifton soil, which had an initial pH of 6.8. Due to the fast release of inorganic N from NutraSweet sludge, the material should be managed as an inorganic, ammoniacal N fertilizer.