Enteric bacteria in aerobically digested sludge.

Indicator bacteria, Salmonella spp., and total aerobic bacteria were determined in samples of undigested sludge and sludge that had been treated by one or two stages of aerobic digestion. Aerobic sludge digestion reduced the level of indicator bacteria by 1 to 2 log10 per g. The level of Salmonella spp. was also reduced during aerobic treatment of sludge. In general, aerobic treatment of sludge reduced, but did not eliminate, indicator bacteria and Salmonella spp.     

Inactivation of poliovirus in digested sludge.

The effect of anaerobically digested sludge on poliovirus during incubation at temperatures between 28 and 4 C was studied. Although virus was fully recoverable from sludge, its infectivity decreased in proportion to the time and temperature of incubation. The rate ranged from greater than 1 log per day at 28 C to about 1 log every 5 days at 4 C. The mechanism of inactivation was studied at the lower temperature where the sedimentation coefficients of most inactivated particles were not detectably modified. The ribonucleic acid (RNA) of these particles appeared to have been nicked and had an average sedimentation value about 70% that of RNA from infectious virus. Since the specific infectivity of RNA from particles recovered from sludge was directly proportional to that of the particles from which it was extracted, loss of infectivity was probably due to inactivation of RNA. Some breakdown was also found in the two largest viral proteins of inactivated particles. Thus, the mechanism of inactivation may be cleavage of viral proteins followed by nicking of encapsulated RNA. Because no virucidal activity was found in raw sludge, this component of digested sludge appears to be a product of the digestion process.     

Inactivation of poliovirus in digested sludge.

The effect of anaerobically digested sludge on poliovirus during incubation at temperatures between 28 and 4 C was studied. Although virus was fully recoverable from sludge, its infectivity decreased in proportion to the time and temperature of incubation. The rate ranged from greater than 1 log per day at 28 C to about 1 log every 5 days at 4 C. The mechanism of inactivation was studied at the lower temperature where the sedimentation coefficients of most inactivated particles were not detectably modified. The ribonucleic acid (RNA) of these particles appeared to have been nicked and had an average sedimentation value about 70% that of RNA from infectious virus. Since the specific infectivity of RNA from particles recovered from sludge was directly proportional to that of the particles from which it was extracted, loss of infectivity was probably due to inactivation of RNA. Some breakdown was also found in the two largest viral proteins of inactivated particles. Thus, the mechanism of inactivation may be cleavage of viral proteins followed by nicking of encapsulated RNA. Because no virucidal activity was found in raw sludge, this component of digested sludge appears to be a product of the digestion process.     

Fungal degradation of anaerobically digested sewage sludge

Fifty isolates of fungi were screened for their ability to grow on and degrade sludge. Cunninghamella elegans was selected for further study of degradation as affected by moisture, nutrients, time and temperature. Maximal sludge degradation (total dry weight basis) was 5.8% by Rhizopus oligosporus, 5.4% by C. elegans and 5.3% by Myrothecium verrucaria, representing approximately 11% degradation of the organic matter present. Added nutrients had little or no effect on sludge degradation. Maximal sludge degradation by C. elegans occurred in three weeks at 30–35 C or four weeks at 25 and 40 C.Sewage sludge is a stable humic material that breaks down slowly with time when mixed with soil. The disposal of sewage sludge is one of the problems of environmental pollution throughout the world. Approximately 455,000 cubic meters of sewage sludge are produced daily in the United States (7). The development of supplementary methods of sewage treatment to be used in tandem with anaerobic digestors are of current interest. Benefits of such a tandem system utilizing fungi would be the acceleration of recycling of waste, supplemental detoxification of sludge, and perhaps even recovery of utilizable protein. The use of fungi to accelerate sludge degradation with the possible side benefits of production of protein or other recoverable metabolites has not been investigated. This paper reports the screening of fifty fungi for their ability to grow on and degrade anaerobically digested sewage sludge and the determination of the level of protein produced by C. elegans on this medium.Portions of this investigation were submitted to Auburn University by W.M.H. in partial fulfillment of the requirements of the M.S. degree.Research and Technology of the U.S. Department of the Interior through the Water Resources Research Institute of Auburn University Project A-030-Ala.     

The influence of factors on dewaterability of one-stage autothermal thermophilic aerobically digested sludges

One-stage auto thermophilic aerobic digestion (ATAD) could achieve the same sludge stabilization efficiency as two- or multi-stage ATAD process does. However, the dewaterability of sludge might be affected through thermophilic digestion because of the release of intracellular substances under the thermophilic temperatures. This paper investigated which operation factors affect intracellular substances released in the liquid phase of sludge that lead to different extent of dewaterability. The results showed that optimal digestion time needs to be prolonged up to 480 h to avoid a deteriorated dewaterability phase. The deterioration in dewaterability of the sludge could be minimized at a retention time of 360 h (i.e., 15 days) under a digestion temperature of 65 °C. Specific capillary suction time (SCST) had quadratic correlations with SCOD, protein (PN) and polysaccharides (PS) in the liquid phase. The coefficient between SCST and the ratio of PN/PS had a value of 0.9764, indicating that the sludge dewaterability was significantly deteriorated by biopolymer of protein and polysaccharides in supernatant.     

Anaerobic biodegradation of phenolic compounds in digested sludge.

We examined the anaerobic degradation of phenol and the ortho, meta, and para isomers of chlorophenol, methoxyphenol, methylphenol (cresol), and nitrophenol in anaerobic sewage sludge diluted to 10% in a mineral salts medium. Of the 12 monosubstituted phenols studied, only p-chlorophenol and o-cresol were not significantly degraded during an 8-week incubation period. The phenol compounds degraded and the time required for complete substrate disappearance (in weeks) were: phenol (2), o-chlorophenol (3), m-chlorophenol (7), o-methoxyphenol (2), m- and p-methoxyphenol (1), m-cresol (7), p-cresol (3), and o-, m-, and p-nitrophenol (1). Complete mineralization of phenol, o-chlorophenol, m-cresol, p-cresol, o-nitrophenol, p-nitrophenol, and o-, m-, and p-methoxyphenol was observed. In general, the presence of Cl and NO2 groups on phenols inhibited methane production. Elimination or transformation of these substituents was accompanied by increased methane production, o-Chlorophenol was metabolized to phenol, which indicated that dechlorination was the initial degradation step. The methoxyphenols were transformed to the corresponding dihydroxybenzene compounds, which were subsequently mineralized.     

Rheological characteristics of highly concentrated anaerobic digested sludge

Highly concentrated anaerobic sludge digestion is a favorable way to treat a considerable quantity of sewage sludge and recover biogas from both environmental and energetic point of view. For enhancing mass transfer and ensuring efficient anaerobic digestion, pumping and mixing are crucial operations which are directly conditioned by the rheology of sludge. The present work aims at studying the rheological characteristics of highly concentrated anaerobic digested sludge with TS (total solid) content more than 8%. The dependence on both TS content and temperature is investigated, respectively, in dynamic and flow measurements. The results show a shear-thinning behavior with a yield stress under flow measurements and a viscoelastic property in dynamic measurements, comparable to a pasty material. The Herschel–Bulkley model can describe these experimental results and a master curve is then proposed. In addition, the yield stress as well as cohesion energy increase with TS content following a power-law. The effect of temperature is relatively smaller, as a consequence of pronounced internal interactions strengthening the interior structure after the digestion, in the form of networks and steric linking.     

Fungi in soils over which digested sewage sludge has been spread

The literature describing the use of sewage in various stages of treatment as well as sewage sludge, both settled and digested, as irrigation or fertilizer supplements is reviewed. A project is described in which anaerobically digested sewage sludge was added to a field in northwestern Pennsylvania, and aerobically digested sewage sludge was added to a field in southeastern Pennsylvania. Samples of soil were taken immediately before this addition, and immediately afterward. Samples were taken at weekly intervals for five months and all were tested for the presence of fungi. From these samples 95 species or species groups of fungi were reported of which several represent species known to produce plant disease. The extent to which populations of such fungi could build up in soils to which sewages or sludges are added frequently is unknown.

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Zusammenfassung Die Literatur, die den Gebrauch des Kloakenwassers in verschiedenen Etappen der Behandlung so wie auch diejenigen, welche die Benützung des bearbeiteten und des verdauten Sediments, als ein Supplement der Irrigation oder der Düngung beschreiben, ist kritisch nachgeprüft worden. Ein Projekt ist beschrieben, in welchem ein anaerob verdautes Kloakenwasser-Sediment an einem Feld in Norwest-Pennsylvania und ein aerob verdautes Kloakenwasser-Sediment an einem anderen in Südost-Pennsylvania verwendet wurde. Proben vom Erdboden wurden unmittelbar vor und nach der Verwendung des Materials entnommen. Dieser Prozess ist wöchentlich für fünf Monate wiederholt und für die Gegenwart von Pilzen untersucht. Von diesen Proben sind 95 Arten oder Artgruppen von Pilzen berichtet, von denen mehrere bekannt sind, daß sie Pflanzenkrankheiten verursachen. Der Umfang, zu welchem Grade solche Pilze eine Verbreitung im Erdboden finden können, zu welchem Kloakenwasser oder dessen Sediment hinzugefügt war, ist häufig unbekannt.

     

Enteric viruses in the Danube river water and sludge.

A study of the viral pollution of the Roumanian course of the Danube river was carried out from 1972 to 1974. The presence of enteric viruses was investigated in 123 water samples, taken by the gauze swab method and in 116 sludge samples from the bottom of the river. The samples were collected from 20 sampling points along the river from Moldova Veche to Br?ila, in accordance with the water use and the main pollution sources. Viruses were recovered from 17.5% of the samples. The frequency of virus isolations from water samples was similar to that observed in sludge samples. Therefore, the viral pollution of the Romanian course of the Danube showed a low level in comparison with other rivers, though two concentration techniques into suckling mice and into tissue cultures, were used for each sample.     

Biological testing of a digested sewage sludge and derived composts

Aiming to evaluate a possible loss of soil habitat function after amendment with organic wastes, a digested sewage sludge and derived composts produced with green residues, where biologically tested in the laboratory using soil animals (Eisenia andrei and Folsomia candida) and plants (Brassica rapa and Avena sativa). Each waste was tested mimicking a field application of 6ton/ha or 12ton/ha. Avoidance tests did not reveal any impact of sludge and composts to soil biota. Germination and growth tests showed that application of composts were beneficial for both plants. Composts did not affect earthworm's mass increase or reproduction, but the highest sludge amendment revealed negative effects on both parameters. Only the amendment of composts at the highest dose originated an impairment of springtails reproductive output. We suggest that bioassays using different test species may be an additional tool to evaluate effects of amendment of organic wastes in soil. Biological tests are sensitive to pollutants at low concentrations and to interactions undetected by routine chemical analysis.     

Stalked bacteria in activated sludge

Summary A laboratory-scale activated sludge unit was fed continuously with a simulated industrial wastewater, consisting of a dilute solution of inorganic salts, at a rate giving a mean retention time of about 3 days. The system produced a well-settling sludge which on examination by electron microscopy was found to contain considerable numbers of stalked bacteria. These were identified as Caulobacter, which have the ability to attach to surfaces and other organisms by means of a prosthecal holdfast and to flourish in waters with a low content of organic nutrients, and whose occurrence in activated sludge has not apparently been previously recorded. Conditions advantageous to Caulobacter generally prevail in activated sludge systems when these operate in growth phases tending to produce well-settling sludge. Since their holdfast gives Caulobacter the ability to initiate and enlarge microbial clusters by attachment, it is suggested that Caulobacter contribute to microbial floc-formation in activated sludge.     

Modeling and optimization of anaerobic digested sludge converting starch to hydrogen

The pH and hydraulic retention time (HRT) of a chemostat reactor were varied according to a central composite design methodology with the aim of modeling and optimizing the conversion of starch into hydrogen by microorganisms in an anaerobic digested sludge. Experimental results from 23 runs indicate that a maximum hydrogen production rate of 1600 L/m(3)/d under the organic loading rate of 6 kg starch m(3)/d obtained at pH = 5.2 and HRT = 17 h. Throughout this study, the hydrogen percentage in the biogas was approximately 60% and no methanogenesis was observed. while the reactor was operated with HRT of 17 h, hydrogen was produced within a pH range between 4.7 and 5.7. Alcohol production rate was greater than hydrogen production rate if the pH was lower than 4.3 or higher than 6.1. Supplementary experiments confirm that the optimum conditions evaluated in this study were highly reliable; while a hydrogen production yield of 1.29 l H(2)/g starch-COD was obtained. An examination of the response surfaces, including hydrogen, volatile fatty acids (VFA) and alcohols production, led us to the belief that clostridium sp. predominated in the anaerobic hydrogen-producing microorganisms in this study. Experiment results obtained emphasize that the response of metabolites was a more useful indicator than hydrogenic activity for obtaining efficient hydrogen production. Furthermore, expressions of contour plots indicate that Response-Surface Methodology may provide easily interpretable advice on the operation of a hydrogen-producing bioprocess.     

Change in cotton plant quality in response to application of anaerobically digested sewage sludge

Treated municipal sewage sludge (TSS) was applied to the cotton plant at rates of 10, 20 and 30 t/ha per year. Seed cotton yield (71.4%), lint yield (67.7%) and cottonseed yield (74.1%) were increased significantly when sludge was applied at a rate of 30 t/ha (TSS3). The effects of TSS applications on seed yield, lint yield and cottonseed yield were listed as TSS3 > TSS2 > CF > TSS1 > C according to the applications. The increasing TSS levels had a positive effect and increased the total N concentration compared to the control. The highest N value was observed in TSS3 plots, while the lowest value was recorded in control (C) plots. The highest P value was found in control (C) at 0.80% and in 10 t/ha (TSS1) at 0.80%, while the lowest value was found in the TSS2 application (0.70%). The K concentration of cottonseed increased with the increasing TSS rates, from 1.56% in control plots to 2.20% in 20 t/ha application (TSS2). Corresponding to the TSS levels, the calcium of plant tissues was determined by a range of 0.12–0.13%. The treatments of TSS and mineral fertilizer had similar effects on the Mg content of cottonseed, which was in the range of 0.38–0.43%. Na content in plant tissue increased with increasing dose of sludge application compared to control soils. Increasing doses of TSS had no significant effect on the concentrations of iron (Fe), copper (Cu), zinc (Zn), manganese (Mn) and boron (B) in cottonseed. The order of the elements with respect to their amounts in cottonseed was as follows: Fe > Zn > Na > B > Mn > Cu. The concentrations of non-essential elements (Ni, Cd, Cr, Pb, Hg and As) in cottonseed were below the permissible limits.     

Ca2+ augmentation for enhancement of aerobically grown microbial granules in sludge blanket reactors

Two sequential aerobic sludge blanket reactors were concurrently operated to examine the effect of Ca²⁺ augmentation on aerobic granulation. Augmentation with 100 mg Ca²⁺ l^–1 significantly decreased the time to cultivate aerobically grown microbial granules from 32 d to 16 d. Ca²⁺-fed granules were denser and more compact, showed better settling and strength characteristics, and had higher polysaccharide contents.     

Transformation of indole by methanogenic and sulfate-reducing microorganisms isolated from digested sludge

In the present study, mineralization of an aromaticN-heterocyclic molecule, indole, by microorganisms present in anaerobically digested sewage sludge was examined. The first step in indole mineralization was the formation of a hydroxylated intermediate, oxindole. The rate of transformation of indole to oxindole and its subsequent disappearance was dependent on the concentration of inoculum and indole and the incubation temperature. Methanogenesis appeared to be the dominant process in the mineralization of indole in 10% digested sludge even in the presence of high concentrations of sulfate. Enrichment of the digested sludge with sulfate as an electron acceptor allowed the isolation of a metabolically stable mixed culture of anaerobic bacteria which transformed indole to oxindole and acetate, and ultimately to methane and carbon dioxide. This mixed culture exhibited a predominance of sulfate-reducers over methanogens with more than 75% of the substrate mineralized to carbon dioxide. The investigation demonstrates that indole can be transformed by both methanogenic and sulfate-reducing microbial populations.     

The efficiency of concentration methods used to detect enteric viruses in anaerobically digested sludge

The presence of enteric viruses in biosolids can be underestimated due to the inefficient methods (mainly molecular methods) used to recover the viruses from these matrices. Therefore, the goal of this study was to evaluate the different methods used to recover adenoviruses (AdV), rotavirus species A (RVA), norovirus genogroup II (NoV GII) and the hepatitis A virus (HAV) from biosolid samples at a large urban wastewater treatment plant in Brazil after they had been treated by mesophilic anaerobic digestion. Quantitative polymerase chain reaction (PCR) was used for spiking experiments to compare the detection limits of feasible methods, such as beef extract elution and ultracentrifugation. Tests were performed to detect the inhibition levels and the bacteriophage PP7 was used as an internal control. The results showed that the inhibitors affected the efficiency of the PCR reaction and that beef extract elution is a suitable method for detecting enteric viruses, mainly AdV from biosolid samples. All of the viral groups were detected in the biosolid samples: AdV (90%), RVA, NoV GII (45%) and HAV (18%), indicating the viruses'' resistance to the anaerobic treatment process. This is the first study in Brazil to detect the presence of RVA, AdV, NoV GII and HAV in anaerobically digested sludge, highlighting the importance of adequate waste management.     

Toxic effects of digested, composted and thermally-dried sewage sludge on three plants

In order to evaluate potential toxic effects of stabilized sewage sludge that are currently applied to agricultural soils, three types of municipal sewage sludge and one pig slurry were subjected to phytotoxicity assays using three plants (Brassica rapa, Lolium perenne and Trifolium pratense). Equivalent batches of aerobically and anaerobically-digested sludge (F) from two municipal wastewater treatment plants, were composted (C) or thermally dried (T). In addition, one anaerobically-digested and thermally-dried pig slurry (P) was tested. A seedling growth test was performed in accordance with the OECD Guideline 208A, using seed emergence and shoot length as endpoints to identify the inhibition of plants growing in increasing doses of sludge. A correlation analysis between EC50 and physico-chemical parameters or the pollutant burden of the biosolids was also calculated. In all tests, lower germination rates were observed for T. pratense than for L. perenne and B. rapa. A moderate stimulatory effect on shoot length at low doses was observed for the three plants. In these wastes, a strong positive correlation was found between higher values of EC50 (less toxicity) and the stability degree of their organic matter, and a negative correlation between EC50 and total N, hydrolysable N or NH4-N content. No correlations were found with heavy metal or organic pollutant content in those wastes. Results indicate that digested sludge, thermally-dried sludge and thermally-dried pig slurry have non-negligible short term phytotoxic effects, and confirm that composting is an effective sludge treatment for the reduction of phytotoxicity.