Leachate post-treatment by electrocoagulation process: Effect of polarity switching and anode-to-cathode surface area.

In the electrocoagulation process, passivation or corrosion of the electrodes is one of the biggest challenges that cause a drop in treatment effectiveness. In this study, the effect of polarity switching was investigated, for the first time, in an attempt to enhance electrocoagulation treatment's ability to remove chemical oxygen demand (COD) and color from pretreated landfill leachate. Moreover, the ratio of the anode to cathode surface area and rotating electrode were examined in light of experimental results. The effect of different parameters, including the stirring speed, initial leachate pH, electrical current density, anode to cathode surface area ratio, and polarity switching time on system efficiency, was evaluated using the one-factor-at-a-time (OFAT) classical method. According to the results, polarity switching resulted in an almost 18% increase in COD removal, 14% increase in color removal, 13% decrease in electrical energy consumption (EEC), 51% decrease in the specific sludge production (TSS/COD), and improved electrode performance compared to non-polarity switching mode. The findings of this research showed the highest COD and color removal efficiencies, which were 34% and 67%, respectively, in a 120 min period, a stirring speed of 135 rpm, the initial leachate pH of 9, the current density of 14.4 mA/cm2, the anode/cathode surface ratio of 0.35, and the polarity switching time of 300 s.

Reducing excess sludge volume in sequencing batch reactor by integrating ultrasonic waves and ozonation.

The effects of ultrasonic waves and ozonation on the reduction of produced sludge in the sequencing batch reactor (SBR) system were investigated in laboratory-scale experiments. For this purpose, the optimal ozone dosage was determined by measuring soluble chemical oxygen demand (SCOD), protein concentration, turbidity level, and biomass yield coefficient. Next, the effect of its integration with different levels of ultrasonic specific energy was evaluated. Based on the results, the minimum excess sludge production in the SBR system was achieved at the ozone dosage of 11 mg O3/g MLSS followed by ultrasonic specific energy of 12000 kJ/kg TS. In this case, the biomass yield coefficient decreased from 0.75 in the control reactor to 0.34 mg MLSS/mg COD in the test reactor, which was equal to a 54% reduction in excess sludge production in the SBR system. In these circumstances, the removal efficiencies of COD, total nitrogen, and total phosphorus were measured as 90%, 82%, and 81%, respectively.

Solid-state anaerobic co-digestion of organic fraction of municipal waste and sawdust: impact of co-digestion ratio, inoculum-to-substrate ratio, and total solids.

Municipal solid waste contains mainly organic wastes that can be a good source for anaerobic digestion. Solid-state anaerobic digestion is an affordable and suitable technique to mitigate the organic fraction of municipal solid waste (OFMSW). However, as the organic loading of OFMSW is high, co-digestion with other materials can improve the system's performance. This study aimed to investigate the performance of the co-digestion of OFMSW and sawdust and study the parameters affecting its performance. Based on the experiments, the optimum sawdust/OFMSW ratio was achieved 1:2 with the methane production of 0.3 L/g VS. In addition, the inoculum-to-substrate ration (I/S) was investigated at 1:4, 1:2, 1:1, 2:1 ratios. The best result was obtained at 2:1 ratio with a total methane yield of 0.28 L/g VS. The results also indicated that I/S ratios less than 1:1 led to fatty acid accumulation and acidic pH condition. The effect of total solids content on the co-digestion process was also examined in this study. According to the results, as the total solids increased, the biomethane yield decreased while the biogas content increased.

Remediation of nitrate-contaminated groundwater by PRB-Electrokinetic integrated process.

Activated carbon is used as a reactive media in Permeable Reactive Barrier (PRB) for the removal of inorganic contaminants such as nitrate from groundwater. Since removal rate by this media decreases by time and due to the high costs of excavation and replacement of new media, the usage of activated carbon as an adsorbent in PRB is limited. The present study aimed to solve this defect by integrating electrokinetic process and PRB, using in-situ regeneration of activated carbon. This research was carried out on a laboratory scale using synthetically contaminated water and modified activated carbon as a reactive media in PRB. The effects of pH, nitrate concentration, carbon to sand ratio, and also electric gradient on the performance of the process were evaluated, and optimal conditions were determined, to increase the system longevity. According to the results, by applying an electric gradient of 1.25 V cm-1 to the PRB alone process in optimum operating condition (135 mg L-1 initial nitrate concentration, flow rate of 2.3 L min-1, pH = 6.8, and carbon to sand ratios of 1:1) the adsorbent capacity increased by 90%. Under these conditions, the integrated process could keep nitrate concentration in the effluent below the standard limit for about 111 h, while the PRB alone process could do the same job for about 59 h. Also, SEM analysis showed that by applying electrokinetic process, activated carbon was regenerated. Integration of electrokinetic process and PRB was also caused nitrate to transfer from activated carbon media into the soil layer above the system. This nitrate-rich soil has the potential for reuse in agricultural activities.

Full scale performance of compost's leachate treatment by biological anaerobic reactors.

A wide range of treatment processes have been applied to leachate treatment with varying success. The aim of this research was to examine the performance of two hybrid biological anaerobic reactors in a new full-scale leachate treatment plant in Rasht composting facility, north of Iran. The studied plant was operated for nearly 12 months and treated up to 50 m(3) day(-1) of fresh compost leachate with a relatively high BOD(5) to COD ratio of around 0.5. The average COD of the raw leachate was measured to be 81 000 mg L(-1). 30% of effective volume of each reactor was filled with clay blocks with a specific area of 87 m(2) m(-3) as the fixed bed. The sequencing of reactors was down flow and up flow, respectively. The maximum COD removal efficiency of 91% was achieved with 4.5 kg COD m(-3 )day(-1) of organic loading rate and 7500 mg L(-1) of volatile suspended solids. There was no significant difference in COD removal efficiency when the reactors were operated with an organic load between 2 and 5 kg COD m(-3 )day(-1). Increasing the volumetric organic loading rate to greater than 6 kg COD m(-3 )day(-1) caused a considerable reduction of COD removal efficiency. The COD removal efficiency decreased to less than 70% when the organic load rose to 10.8 kg COD m(-3 )day(-1). Nevertheless, hybrid anaerobic reactors proved to be a feasible technique for the reduction of organic load from the composting leachate which was the subject of this study.

Effect of process variables on the production of Polyhydroxyalkanoates by activated sludge.

Polyhydroxyalkanoates are known to be temporarily stored by microorganisms in activated sludge, especially in anaerobic-aerobic processes. Due to the problems resulted from the disposals of plastic wastes and excess sludge of wastewater treatment plants, the production of polyhydroxyalkanoates by treating activated sludge and determining the effect of process variables were the main issues of this paper. In this research, an anaerobic-aerobic sequencing batch reactor was used to make microorganism adapted and a batch aerobic reactor was used for enriching them. The variables affecting polyhydroxyalkanoates production including aeration time, sludge retention time, and volatile fatty acids concentration of the influent in sequencing batch reactor, and also carbon to nitrogen ratio and cultivation time in polymer production reactor, were investigated using Taguchi statistical approach to determine optimum conditions. The maximum polymer production of 29% was achieved at sludge retention time of 5-10 days, aeration time of 2 hours, supplementation of 40% of volatile fatty acids in the influent and increasing of carbon to nitrogen ratio of polymer production reactor to above 25 g/g. Based on the results, in optimum conditions, the volatile fatty acids concentration which increased the production of polyhydroxyalkanoates up to 49% was the most effective variable. Carbon to nitrogen ratio, sludge retention time and aeration time were ranked as the next affecting parameters. Although the polyhydroxyalkanoates content achieved in present study is much lower than that by pure culture, but the proposed method may still serve well as an environmental friendly means to convert waste into valuable product.

Report: future industrial solid waste management in pars Special Economic Energy Zone (PSEEZ), Iran.

The Pars Special Economic Energy Zone (PSEEZ) is located in the south of Iran, on the northern coastline of the Persian Gulf. This area was established in 1998 for the utilization of south Pars field oil and gas resources. This field is one of the largest gas resources in the world and contains about 6% of the total fossil fuels known. Petrochemical industries, gas refineries and downstream industries are being constructed in this area. At present there are three gas refineries in operation and five more gas refineries are under construction. In this study, different types of solid waste including municipal solid waste (MSW) and industrial wastes were investigated separately. The aim of the study was to focus on the management of the industrial wastes in order to minimize the environmental impact. In the first stage, the types and amounts of industrial waste in PSEEZ were evaluated by an inventory. The main types of industrial waste are oil products (fuel oil, light oil, lubricating oil), spent catalysts, adsorbents, resins, coke, wax and packaging materials. The waste management of PSEEZ is quite complex because of the different types of industry and the diversity of industrial residues. In some cases recycling/reuse of waste is the best option, but treatment and disposal are also necessary tools. Recently a design has been prepared for a disposal site in PSEEZ for the industrial waste that cannot be reused or recycled. The total surface area of this disposal site where the industrial waste should be tipped for the next 20 years was estimated to be about 42 000 m2.