A novel laboratory method to determine the biogas potential of iron-dosed activated sludge

Sludge biogas potential is often reduced by iron-dosing, the extent of the reduction being related to the nature of the sludge and the dosing process. The aim of this research was to develop a rapid laboratory method to measure the impact of iron-dosing on the biogas potential of activated sludge, taking into account the mechanisms that may be decreasing biogas yield. To validate the method, sequential extraction (SE) was used to fractionate iron and phosphorus in the sludge before and after iron-dosing. The laboratory-dosing regime increased total iron and phosphorus in the sludge but decreased their bioavailability, producing sludge with a similar inorganic composition to full-scale chemical P removal (CPR) sludge. Laboratory-dosed sludge produced 12–20% less biogas and 9–21% less methane when anaerobically digested, in comparison to the same undosed sludge. This method should help water companies and academics to more closely simulate iron-dosing in the laboratory.     

The operating line for activated sludge

The mass balance for O2 on an activated sludge process has been re-arranged to identify the O2 limited boundary for any given treatment installation and for any combination of feed flow rate and input bCOD. The boundary is described graphically as the operating line.     

The occurrence of fungi in activated sludge

The population of a biological system in a sewage treatment plant is formed of a fortuitous assemblage of microorganisms, members of which are continually dropped out while additional members are recruited. Many of these organisms are active throughout the year. Fewer yeasts than filamentous fungi are found by the plating technique. The population is about evenly divided between species producing their spores in dry states and in wet states. The fungus population includes species which under certain circumstances are able to use a wide variety of substrates from simple sugars to complex carbohydrates and hydrocarbons.

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Zusammenfassung Die Population eines biologischen Systems in einem Kloakenwasser-Behandlungs-werk ist durch ein zufälliges Zusammentreffen von Mikroorganismen geformt, deren Mitglieder fortwährend ausfallen, während andere hinzukommen. Viele dieser Mikroorganismen sind während des ganzen Jahres aktiv. Weniger Hefen denn Fadenpilze sind mit der Plattentechnique gefunden. Die Population ist ungefähr gleichmäßig unter den Arten verteilt, die die Sporen in trockenem wie in feuchtem Zustand produzieren. Die Pilzpopulation umfaßt Arten, die unter gewissen Umständen fähig sind, eine große Varietät von Nährmaterial, von einfachen wie auch komplexen Kohlenstoffhydraten und Kohlenstoffhydraten zu benutzen.

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Much of the material included here was Presented at the 23rd Industrial Waste Conference Purdue University, Lafayette, Indiana May 7–9, 1968     

The removal of Salmonella enteritidis in activated sludge

Salmonella destruction efficiencies of 99% were obtained after 10 h aeration at 15°C in a laboratory model of the activated sludge process. This study demonstrated that, in a batch process, the removal of salmonellas occurred in three phases. (i) By 4 h, 90% of the original inoculum had disappeared from the activated sludge, probably due mainly to predation by ciliated protozoa. The remaining 10% was distributed between the liquid phase (approximately 90%) and the sludge floc (approximately 10%). (ii) During the next 2 h this situation was inverted so that, by 6 h, more than 80% of the remaining salmonellas were then adsorbed to floc, leaving less than 20% in liquid suspension. (iii) From 6 h onwards there was a much slower decline of the remaining salmonellas attached to floc. The addition of dioctyl sodium sulphosuccinate after 4 h, inactivated the ciliated protozoa populations and completely eliminated the continued reduction of salmonellas from activated sludge observed previously.     

Mycoflora of activated sewage sludge

Thirty-eight species of fungi were identified in pure culture after isolation from activated sewage sludge by serial dilution. Nine species and genera were identified that had not been previously reported.In 1963, Cooke (1) published an excellent laboratory guide on the identification of fungi from polluted water, sewage, and sewage treatment systems; of approximately 30 papers cited only one (2) dealt with fungi from activated sewage sludge. Later (1970), Cooke & Pipes (3) enumerated 47 fungi consisting of 4 genera of yeasts and 33 genera of filamentous fungi that had been isolated from activated sludge. This paper reports the mycoflora of anaerobically digested sludge from a residential area in Auburn, Alabama.     

Enzymatic activities of activated sludge

Summary As a potential measure of active biomass in an automated and continuous system, enzyme activities of activated sludge were sought that would allow a rapid and accurate determination. Using p-nitrophenylphosphate, bis-p-nitrophenylphosphate, p-nitrophenyl-- and -D-gluco- or galactopyranosides, and the p-nitroanilides of L-alanine, L-leucine, L-lysine, L-glutamic acid and L-phenylalanine, we could establish that the corresponding phosphatase, cyclic phosphodiesterase, glycosidase and aminopeptidase activities can be conveniently tested with diluted activated sludge within 10–20 min incubation at 30°C. The reactions were linear with time and concentration of activated sludge. The specific activities were in the range from 1 to 50 nmol substrate cleaved/min/mg protein at 30°C. They were diminished by starvation or poisoning with zinc powder, ZnCl₂, HgCl₂ or KCN. The enzymes were over 95% sedimented together with the flocs. Comparable activities were found in sludges from three independent sewage works in the Munich area. At the same time, dehydrogenase activities and ATP contents were investigated under several conditions.     

Aeration of concentrated activated sludge

A multiphase project has been planned to develop a new biological process capable of economically treating high BOD wastes. Herein is presented the results of the first phase of the program, in which the feasibility of growing concentrated microbial cultures was investigated and the oxygen and power requirements for maintaining such cultures were determined. An example is given of the scale-up of power requirements for oxygen transfer in a prototype system.     

Structure of activated sludge floes

Relatively large activated sludge floes (larger than about 100 mum) were stabilized, using a histological tissue specimen preparation procedure, and then were sliced into sections of 3 to 6 mum thick. The study of these sections, after staining, revealed the internal structure of the activated sludge floes. No uniformity of this structure was found. The distribution of microorganisms and of extracellular polymers (EPs) in the floes varied randomly on the plane of the sections and along the dimension perpendicular to the plane, leaving large water channels and reservoirs in some of the floes. The lack of a characteristic size for the water gaps in the floes and a general self-similar appearance of the sections suggested that the activated sludge floes might be characterized by the fractal concept within a certain size limit. Direct observation of the interior of the floes indicated an abundant presence of extracellular polymers (EPs) in amorphous forms, surrounding microorganisms in most of the floes.     

Enhancement of the activated sludge process by activated carbon produced from surplus biological sludge

Surplus biological sludge from wastewater treatment operations was converted into activated carbon and then added to the aerated vessel of an activated sludge process treating phenol and glucose. The addition of activated carbon, either sludge-based or commercial, enhanced phenol removal from 58 to 98.7% and from 87 to 93% for COD with feed concentrations of 100 mg phenol l^–1 and 2500 mg COD l^–1. No differences were found between the activated sludge-activated carbon bench scale continuous reactors operating with either commercial or sludge-based activated carbon in spite of the higher adsorption capacity of the former.     

Filamentous organisms in activated sludge

Activated sludge, as an aerobic environment rich in organic matter, often provides the optimum conditions for the development of colourless filaments. From the taxonomic point of view, these colourless filaments can be divided into three groups of basic characteristics: bacteria, cyanophyceae and fungi. The effort to distinguish these three groups is not only inspired by the endeavour to classify them taxonomically correctly, but rather by possible different physiological efficiencies of the individual groups. This may be their basic significance for the determination of technical parameters of the activated sludge process.     

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.     

Upgrading activated sludge systems and reduction in excess sludge

Most of 200 Activated Sludge Plant in Iran are overloaded and as a result, their efficiency is low. In this work, a pilot plant is manufactured and put into operation in one of the wastewater treatment plants in the west of Tehran. Instead of conventional activated sludge, a membrane bioreactor and an upflow anaerobic sludge blanket reactor used as a pretreatment unit in this pilot. For the sake of data accuracy and precision, an enriched municipal wastewater was opted as an influent to the pilot. Based on the attained result, the optimum retention time in this system was 4h, and the overall COD removal efficiency was 98%. As a whole, the application of this retrofit would increase the plant's capacity by a factor of 5 and reducing the excess sludge by a factor of 10. The sludge volume index in the anaerobic reactor was about 12 after granulation occurred.     

Separation of polymer from activated sludge

Summary A simple large-scale method of separating polymer from activated sludge by shear, using a continuous centrifuge, is given.     

Role of phosphorus in activated sludge

Monod's kinetic model was used to correlate the specific growth rate of mixed activated sludge with the limiting substrate of phosphorus for both batch and continuous-flow culture systems. In the batch reactor system, the specific growth rate varied from 0.092 to 0.617 h(-1) and the saturation constant changed from 25.5 to 117.5 when the COD: P ratio was controlled within the range of 10 to 788 and at the temperature 25+/- 0.5 degrees C. An inverse relationship between specific growth rate and cell yield was found. the maximum specific growth rate and the saturation constant obtained from this study were equal to 0.64 h(-1) and 0.378mg/L, respectively. In the completely mixed continuous-flow culture system, it was found that the substrate utilization, biological solids production, and sludge composition were markedly affected by the source of phosphorus available in the wastewater. The phosphorus-limited activated sludge is normally high in carbohydrate content and low in protein content. Also, sludge organisms growth under the severely restricted phosphorus condition usually possess a large capsule. These capsulated carbohydrate-like substances can be converted to cellular protein if the source of phosphorus is added. The values of cell yield in the continuous-flow activated sludge system are predictable by the use of kinetic constants that are generated from batch culture studies.