Codigestion of organic wastes is a technology that is increasingly being applied for simultaneous treatment of several solid and liquid organic wastes. The main advantages of this technology are improved methane yield because of the supply of additional nutrients from the codigestates and more efficient use of equipment and cost‐sharing by processing multiple waste streams in a single facility. Many municipal wastewater treatment plants (WWTPs) in industrialized countries currently process wastewater sludge in large digesters. Codigestion of organic wastes with municipal wastewater sludge can increase digester gas production and provide savings in the overall energy costs of plant operations. Methane recovery also helps to reduce the emission of greenhouse gases to the atmosphere. The goal of this literature survey was to summarize the research conducted in the last four years on anaerobic codigestion to identify applications of codigestion at WWTPs. Because the solids content in municipal wastewater sludge is low, this survey only focuses on codigestion processes operated at relative low solids content (slurry mode). Semi‐solid or solid codigestion processes were not included.
 
 Municipal wastewater sludge, the organic fraction of municipal solid waste, and cattle manure (CAM) are the main wastes most often used in codigestion processes. Wastes that are codigested with these main wastes are wood wastes, industrial organic wastes, and farm wastes. These are referred to in this survey as codigestates. The literature provides many laboratory studies (batch assays and bench‐scale digesters) that assess the digestibility of codigestates and evaluate the performance and monitoring of codigestion, inhibition of digestion by codigestates, the design of the process (e.g., single‐stage or two‐stage processes), and the operation temperature (e.g., mesophilic or thermophilic). Only a few reports on pilot‐ and full‐scale studies were found. These evaluate general process performance and pretreatment of codigestates, energy production, and treatment costs.

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A pilot-scale biotrickling filter was installed at the Hyperion Treatment Plant in Los Angeles to study H 2 S/odor and VOC removal from the Headworks' waste air. The performance of the reactor was continuously monitored over a period of 10 months. At an average empty bed gas residence time of 24 s, 10-50 ppm H 2 S was consistently removed at greater than 98% efficiency, corresponding to an average volumetric H 2 S elimination capacity of 5.2 g/m 3 .h. Concentration profiles over the height of the reactor indicated near complete removal in the first section of the reactor and that elimination capacities up to 30 g/m 3 .h could be obtained. The odor reduction was 98%, which corresponded to the efficiency of removal of H 2 S as the major pollutant. VOCs were present at concentrations up to 150 ppb. Low but significant removal of toluene and benzene was observed when the biotrickling filter was operated with pH-control to neutralize sulfuric acid production from H 2 S oxidation. Xylenes and chlorinated VOCs were not removed, irrespective of experimental conditions in the reactor. The results lead to the conclusion that VOC removal is the limiting process in biotrickling filters for the simultaneous removal of H 2 S and VOCs at POTWs.

To assess the pollution effects of detergents in Tehran ground water aquifer, from December 1974 to September 1975, out of 3756 wells within metropolitan Tehran, 316 wells were selected according to simple random sampling without replacement. Samples from the ground water were analyzed for concentration of detergents by Methylene Blue Colorimetric Method.The conclusion asserted is that with a confidence limit of 95°70, standard error of 2, and permissible error of ! 0 . 0 0 5 , the average concentration of detergents in Tehran ground water aquifer is within 0.1593 to 0.1163 mg 1 -l as MBAS.

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