Municipal wastewater sludge has been used for fertiliser and biogas production for several decades. Chemical compounds such as iron and aluminium are common coagulants used in wastewater treatment plants to remove suspended solids, phosphorus and micro-organisms. This laboratory study explores whether ferric chloride (FeCl3 as PIX-111) or aluminium chloride (AlCl3 as PAX-18) flocculation could stimulate biogas production in wastewater sludge contaminated with Microthrix parvicella. In a fermentation process run in three replicates, cumulative methane production was in average about 25% higher using the iron flocculated sludge than using the aluminium flocculated sludge; this difference was statistically significant (P<0.05) in the subsequent runs of the semi-continuous process. In all runs, the iron flocculated sludge produced less (P<0.05) hydrogen sulphide in the biogas than the aluminium flocculated sludge. The numbers of M. parvicella stayed at the similar levels throughout the process. It is concluded that biogas production is higher and more stable with iron coagulant in comparison with aluminium coagulant, presumably due to the reduced formation of hydrogen sulphide. Thus, iron coagulants seem to be better than aluminium coagulants to stimulate the methane production process. Both coagulants significantly suppressed multiplication of M. parvicella in the biogas reactor, i.e. they did not evoke foaming in this experiment.

In recent years, Microthrix parvicella has been identified as the main element of sludge bulking in wastewater treatment plants by activated sludge process. Methods: (1) the measurement of lengthy chain of fatty Acids (2) Pilot study.(3) Laboratory Study.(4)Microscopic Study. Results :(1) Microthrix parvicella is a gramm positive bacteria. Its presence in the urban wastewater treatment plants depend on the low Sludge loading (less than 3 grams of the lengthy chain fatty acid for each kilogram of solid material per day.) (2) The critical Growth of the bacteria is being observed at less than 15° Celsius. (3) The utilized main substrate of the bacteria is the lengthy chain fatty acid. (4) The bacteria is being accumulated in sludge foam where there is a suitable place for the Growth of the bacteria.(5) Polyaluminum chloride (PAC) will prevent the Lipase production as well as Enzyme activity of the bacteria, consequently, it has negative effect on the amount of substrate absorption (hydrolysed fats) by the bacteria. If 2 to 3 grams of Al3+ are used for each kilograms of solid material per day, which is selected proportionate to the sludge life, the bacteria can be eliminated completely. (6) If the primary sedimentation is utilized for about 20% eliminated load of the solid material, concerning the remarkable elimination of mentioned bacteria, there is not a noticeable change in the Sludge volume index.

To facilitate the wastewater recycling process while adhering to environmental and industrial regulations, it becomes imperative to meet stringent standards. This necessitates the effective elimination of organic substances, with particular emphasis on nitrogen-based compounds. To this end, activated sludge methods, particularly the step-feed biological nitrogen removal (SFBNR) process, are employed. Although various operational measures are employed in SFBNR systems, including the elimination of complex substrates, modifications in aeration conditions, the utilization of piston hydraulic flow, and the appropriate distribution of substrates, these systems remain susceptible to the excessive growth of filamentous bacteria. The current study aimed to examine the change in the distribution of the hydraulic flow entering this system on a real scale over a period of five years. It was observed that the quality of sludge settling improved and accordingly the overgrowth of filamentous Microthrix parvicella declined, thereby enhancing the quality of the effluent

The aim of this study was the survey of the surface microtriches of Dollfusiella spinulifera reported for the first time from the Persian Gulf. After isolating cestodes from five specimens of Himantura sp., first, the worms were stained for identification, of which, the best specimens were selected, unmounted in Xylene and after destaining finally dried in hexamethyldisilazane and examined with scanning electron microscopy. The results showed that except for the apex and distal bothrial surface, which are covered with papilliform filitriches and acicular filitriches, respectively, other surfaces were adorned with palmate spinitriches and filitriches (papilliform filitriches or acicular filitriches). In addition, the pattern of the surface microtriches was compared between Iranian population of this species from the Persian Gulf and the Australian specimens. The comparison revealed the difference in the Microthrix pattern of these two conspecific allopatric populations.

One of the problems that often happens in activated sludge systems is poor settling and compactibility of sludge in secondry clarifiers. Poor settling of sludge causes decreasing quality of treated wastewater and increasing cost of sludge treatment.In this project, causes of poor settling and compactibility of sludge was determined by experimental method in Zargandeh wastewater treatment plant (Tehran). In the first stage, sludge settling characteristics were determined by caculating sludge volume index (SVI). Because one of the causes of sludge rising and floating is denitrification in the second stage, denirtification phenomenon was investingated by measurment of nitrogen in varius compounds. In the third stage, sludge flocs was investigated by microscope for determining flocs structure and bulking phenomenon and consequently, identificating filamentous bacteria. The dominat bacteria that cause bulking in Zargandeh wastewater treatment plant is M. parvicella and secondary bacteria is type 0092. The growth of these bacteria probably was arised from low F/M, low DOES and completely mixed hydroulic regime of the aeration basin. In the fourth stage, design criteria and operation parameters of the treament plant were controled. The comparsion of these data have shown that this system has hydroulic over load.

This research studied the precipitation of calcium carbonate by populations of bacteria from domestic wastewater cultivated in both natural and artificial solid culture media. The only carbonate-forming bacteria detected appeared in an artificial medium added with calcium acetate. Precipitation occurred three days after inoculation, and the percentage was slightly higher than 65%. Our results showed that nine major carbonate-forming colony types were the dominant heterotrophic platable bacteria growing aerobically in artificial media added with calcium acetate. According to their taxonomic affiliations (based on partial sequencing of the 16S-rRNA), the nine strains belonged to the following nine genera of Gram-negative and Gram-positive bacteria: Caulobacter, Blastomonas, Roseobacter, Staphylococcus, Bacillus, Gemmatimonas, Saccharopolyspora, Microthrix, and Sphingomonas. All of these strains formed calcium carbonate, precipitated as calcite and vaterite in different proportions and shapes (spheres, hemispheres, dumbbells, and pseudopolyhedral forms). The results of this study suggest that in real domestic wastewater, the precipitation of carbonates through bacterial action could not take place in situ because the concentrations of calcium did not create the optimal circumstances for biomineralization. However, in the artificial media, it was possible to induce this process by adding calcium ions.