Procedures of starting up and implementing of subsurface wetlands

Background and Purpose: Subsurface flow wetlands are one of the successful treatment methods used for municipal and industrial wastewater treatment, and are economical in terms of energy consumption and workforce. Much research has been conducted on wetland operation output in wastewater treatment, but no enough information is available on their start-up and maintenance. The present study investigates the circumstance of starting up and implementing a wetland

Methods and Materials: In this experimental study, two subsurface flow wetlands with a two-day detention time and two pretreatment units were built. The former was similar to Primary Settling tank with a 4-hour detention time and the latter was similar to anaerobic pond equipped a with digestion pit with a two-day detention time in a pilot scale. The wastewater [BoD5 = 250 mg/l, Tss=320 mg.l and ph=7.2] from municipal network in Sabzevar, Iran was used for irrigation; the pilot implementation and maintenance took one year

Results: Pilot operation indicated that the principal factors in implementing subsurface flow wetland were temperature, nonpenetrateability of the bed, and wastewater ingredients. However, pretreatment and bed obstruction were the limiting parameters of the wetland maintenance

Conclusion: Pretreatment of the subsurface flow of wetlands does not yield a high output; and if anaerobic ponds equipped with digestion pits are used, the treatment output is significantly enhanced, and the wetland operation will face minimum barriers

Removal of triethylamine vapor from waste gases by biotrickling filter

Sampling of triethylamine in the cold-box unit in an auto-manufacturing company in Iran has indicated the average concentration of 430 mg/m[3] in the emission duct. In this study a biotrickling filter was used for treatment of triethylamine in air stream. Triethylamine removal efficiency [K/L] pattern was evaluated by changing volumetric loading [L], superficial gas velocity [U[o]], empty bed gas retention time [EBRT] and recirculation liquid flow rate [V[L]], while operating at constant temperature of 25 +/- 1 Degree C. For finding the effect of EBRT on the triethylamine removal efficiency, tests were performed at EBRT of 156 s, 52s and 31s and a constant liquid recirculation velocity of 3.466 m[3]/m[2]/h. Results showded that for a test period of 65 days, triethylamine removal efficiencies of more than 98% were obtained for EBRT of 156s and loading rates of less than 48 g/m[3]/h. With an EBRT of 52s removal efficiencies of > 90% were obtained for loadings of < 57 g/m[3]/h and maximum removal capacity was 53.4 g/m[3]/h at volumetric loading of 64 g/m[3]/h. Also with an EBRT of 31 s the maximum removal capacity was 53.6 g/m[3]/h at volumetric loading of 68 g/m[3]/h. Thus in the range of implemented EBRTs the proper absorption of triethylamine from gas to liquid phase took place and the elimination efficiency was shown to be dependent on microorganisms activity rate. The effect of liquid flow rate on the triethylamine removal efficiency was investigated by changing VL in the range of 3.46 to 10.40 m[3]/m[2]/h at EBRT=31 s and influent triethylamine concentration of 600 mg/m[3]. Results showed that the triethylamine removal efficiency was nearly independent of the liquid recirculation rate

Investigation of intermittent chlorination system in biological excess sludge reduction by sequencing batch reactors

The excessive biological sludge production is one of the disadvantages of aerobic wastewater treatment processes such as sequencing batch reactors. To solve the problem of excess sludge production, oxidizing some of the sludge by chlorine, thus reducing the biomass coefficient as well as the sewage sludge disposal may be a suitable idea. In this study, two sequencing batch reactors, each with 20 L volume and controlled by on-line system were used. After providing the steady state conditions in the reactors, sampling and testing of parameters were done during 8 months. The results showed that during the solid retention time of 10 days the kinetic coefficient of Y and Kd were 0.58 mg biomass/mg COD and 0.058/day, respectively. At the next stage, different concentrations of chlorine were used in the reactors intermittently. Results showed that 15 mg chlorine/gMLSS in the reactor was able to reduce the yield coefficient from 0.58 to 0.3 mg biomass/mg COD. In other words, the biological excess sludge was reduced about 48%. But the soluble chemical oxygen demand increased slightly in the effluent and the removal percentage decreased from 95% in the blank reactor to 55% in the test reactor

Cadmium absorption and accumulation in different parts of kidney beans, radishes and pumpkins

This study is done to measure the absorption and distribution of cadmium in different parts of kidney beans, radishes and pumpkins. Three parts of a field was chosen. In one part 65 ppm of cadmium nitrate was added to water and in the other part 130 ppm, the last part was irrigated with normal water. Samples were digested by EPA 3050 method. Cadmium concentration was measured by Unicam 919 absorption unit. Beans accumulate cadmium mostly in root [70 ppm] and a little amount is mobilized through upper parts [12-16ppm], but kidneys did not accumulate a significant amount. In radishes the roots did not accumulate a significant amount of cadmium but stems had 4 ppm and leaves had 25 ppm. Cadmium concentration in soil does not affect its concentration in different parts of pumpkins and beside the stems and leaves [4 ppm] the other parts' concentrations were insignificant. In regard to the results of this study the cadmium concentrations in edible parts of the samples [kidney beans, radish roots and pumpkin fruit] were less than the U.S. EPA standards for agriculture and human beings

Determination of design criteria for UASB reactors as a wastewater pretreatment system in tropical small communities

A pilot scale study was set up to investigate the principle design parameters of up flow anaerobic sludge blanket [UASB] reactors for treating wastewater of small communities in the tropical regions of Iran. A steel pipe with a diameter of 600 mm and a height of 3.6 m was used as the reactor in which a digestion and a 3-phase separator element had a volume of 0.848 and 0.17 m[3] respectively. During this study, which lasted for 203 days, two distinct phases were carried out according to the ambient temperature. The temperature of the wastewater entering the reactor was naturally ranged from 22 to 26 °C and no heat exchanger was used. The hydraulic retention times including 2, 4, 6, 8, and 10 hours with various loading rates of 0.95 to 5.70 kg COD/m[3]/day for colder period and from 1.35 to 6.40 kg COD/m[3]/day for warmer period were examined. On the basis of the results the optimal hydraulic retention time for warmer period with a 2.20 kg COD/m[3]/day organic loading rate was 6 hours which BOD5, COD and TSS removal efficiency were 71, 63 and 65 percent respectively. During the colder period the removal ratio of BOD5, COD and TSS with an optimal hydraulic retention time of 8 hours and organic loading rate of 1.22 kg COD/m[3]/day were 54, 46 and 53 percent respectively