The disposal of excess sludge from wastewater treatment plant represents a rising challenge in activated sludge processes. Hence, the minimization of excess sludge production was investigated by increasing the dissolved oxygen in aeration basin. Units of the pilot include: Primary sedimentation tank, aeration basin, secondary sedimentation tank, and return sludge tank. Volume of aeration basin is 360 l and influent flow rate is 90 L/h. Influent of pilot is taken from effluent of grit chamber of Isfahan's North Wastewater treatment plant. The experiments were done on different parts of pilot during the 5 month of study. Results show that increase of dissolved oxygen in aeration tank affect on decrease of excess sludge. Increase of dissolved oxygen from 0.5 to 4.5 mg/L resulted in 25% decrease of excess sludge. Variation of dissolved oxygen affect on settle ability of sludge too. By increase of dissolved oxygen, SVI decreased and then increased. Value of 1-3 mg/L was the adequate range of dissolved oxygen by settles ability of sludge and optimum range was 2-2.5 mg/L. It could be concluded by increasing of dissolved oxygen up to of 3 mg/L, sludge settle ability significant decreased.

Excess sludge treatment and disposal is a major challenge for wastewater treatment plants worldwide. In this study, sludge reduction was evaluated using pilot scale sequencing batch reactors (SBRs). Two SBRs were operated alongside each other over a period of 12 months during which time measurements were performed to determine COD, MLSS, MLVSS, pH, DO, SV1, SOUR, and ORP. The results showed that among the different SRT durations (5, 10, 15, 20, 25 days), the 10-day sludge retention time yielded maximum COD removal efficiency (90%) without any bulking or foaming problems. Prior to any reactions taking place in the reactor, the sludge was exposed to various oxidation reduction potentials for 1 to 8 hours in order to determine the effects of uncoupling metabolism on biomass production under different anoxic and anaerobic conditions. COD was observed to decrease from 600 to 33 mg/l while MLSS increased from 1350 to 1500 mg/l over a retention time of 7 hours and for an ORP value of -238 mv. The effluent COD obtained as a result of operating this process was below the limits set by environmental regulations for surface waters and reuse in agriculture. For an ORP value of - 238mv, SOUR and SVI were measured to be 22 mgO2/h.gVSS and 40 ml/g, respectively.

This study investigates the application of a thermo-biological approach in the return sludge line of an activated sludge system to reduce excess sludge production and improve overall treatment performance. The effects of increasing the return sludge temperature on pollutant removal efficiency and sludge characteristics were evaluated under real operational conditions. This experimental-analytical study investigated the impact of thermal conditioning of return sludge on pollutant removal efficiency and excess sludge reduction in a full-scale activated sludge wastewater treatment system. Return sludge was heated to 40 °C, 50 °C, and 60 °C, and the system's performance was monitored over 60 days by measuring parameters such as Chemical Oxygen Demand (COD), Total Suspended Solids (TSS), Mixed Liquor Suspended Solids (MLSS), and Sludge Volume Index (SVI). All measurements adhered to APHA standards, and data were analyzed using Analysis of Variance (ANOVA) and descriptive statistics to determine the significance of the observed effects. Experimental results demonstrated that elevating the return sludge temperature to 40°C significantly improved the removal efficiencies of TSS and COD, while also reducing the sludge yield coefficient and enhancing sludge settleability, as indicated by the SVI. Over a 180-day operation period, excess sludge volume and weight were reduced by 47.05% and 36.07%, respectively, at 40 °C. These reductions increased to 56.93% and 62.30% at 50 °C, and to 59.92% and 75.41% at 60 °C. However, effluent quality declined at temperatures above 40°C, highlighting the trade-off between sludge reduction and treatment performance. The optimal operating condition was determined to be a return sludge temperature of 40°C, with a cell retention time of 25 days and a hydraulic retention time of 20 hours, offering the best balance between sludge reduction and effluent quality.

In the present world, in which all people force themselves to follow the environmental regulations, environmental assessment is necessary. For all big projects, there are some challenges in the field of wastewater treatment, specially the activated sludge system. These challenges are about the production and the disposal of excess sludge produced in wastewater treatment plants. Minimization of sludge production in wastewater treatment plant with the activated sludge system by the optimization of treatment parameters is the aim of the present study. For this purpose, a pilot laboratory was installed in the civil engineering department of K.N. Toosi University and the wastewater was supplied from Shahrak-e-Qods wastewater treatment plant.The results obtained form sampling and laboratory tests were noticeable: the excess sludge production reduced by raising the oxygen concentration in the mixed liquid. Also, a decrease in the loading of the sludge entering the aeration tank resulted in a decrease in the produced sludge. Finally, a mathematical model for the simulation of activated sludge floes and the description of the effects of the above-mentioned parameters was developed.

One of the most important problems in activated sludge systems, is the excess sludge production in wastewater treatment plants, in which its stabilization and disposal has attracted the most attention to itself. In this research, several procedures to reduce the sludge in aerated systems, especially in activated sludge system is explained. Some of the procedures are 1. Lysis-Cryptic growth which includes alkaline-thermal treatment, ozonation, chlorination, and increasing dissolved oxygen. 2. Maintenance metabolism 3. Uncoupling metabolism 4. Predation on bacteria. Also in this research, for each of the above mentioned procedures, some examples are provided. In some procedures which are most chemically (such as ozonation and uncoupler additions), the amount of excess sludge is reduced to zero. Therefore, the best solution for elimination of excess sludge, has been known as chemical procedures; although economical considerations should always be taken into account.