عنوان مقاله [English]
The growth in world population, improvement of public welfare and increase in the production of consumer goods, has resulted in increased quantities of solid waste generation. As in other developing countries, in Iran, landfilling is the main method of waste disposal. This preference, in terms of lower costs and simple technology, is justified, as long as measures are undertaken to protect waterways and soil contamination due to leachate discharge. Leachate usually contains high concentrations of organic compounds, such as ammonia N, heavy
metals and inorganic salts, thus, necessitating treatment prior to discharge into the environment.
In this study, Kahrizak landfill leachate treatment was investigated using a 159 L anaerobic hybrid reactor. In addition, an external system (sedimentation tank + recirculation pump) was used for maintaining sludge in the reactor. A heat exchanger was used from the beginning until an organic loading rate (OLR) of 8.1 kg SCOD/$m^3$-d to keep the reactor temperature in the range of 33-37$^o$C.
Because of malfunction, no auxiliary heating was provided after the above-mentioned OLR, and the system was operated at summer room temperature so that the wastewater temperature was 28-31$^o$C. Hydraulic retention time (HRT) was maintained at a constant value of 2.7 days, and the inlet soluble chemical oxygen demand (SCOD) was gradually increased from 9.2 to 67.2 g/L by diluting the leachate. The recirculation system decreased the actual HRT to 13.9 hr and a nominal HRT of 2.7 days. The set up level of flexibility for hydraulic shock loads was decreased, as such, but the recirculation system enabled the system to operate at an increased solids retention time (SRT).
According to the results, pH was in a range from 7.0 to 7.8. This level of pH resulted in a considerable amount of precipitation in the reactor, so that there was an increase of 13.7 kg in total suspended solid mass, while the
volatile part increased just 2.5 kg during the study. This precipitation caused some clogging problems. Maximum SCOD removal efficiency of about 95% was observed at an OLR of 8.1 to 9.7 kg SCOD/$m^3$-d.
At the maximum OLR of 24.9 kg SCOD/$m^3$-d, the leachate was pumped into the reactor without any dilution and a SCOD removal efficiency of 76.3% was obtained. Based on observations during the operation, the system described in this paper has an ability to treat leachate without using additives to adjust pH. A comparison between conventional UASB systems and the system used in this study shows that not only does the current system have a higher OLR capacity, but it can also reduce the biomass loss.