The implementation of data reconciliation for evaluating a full-scale petrochemical wastewater treatment plant

Data reconciliation and mass balance analysis were conducted for the first time to improve the data obtained from a petrochemical wastewater treatment plant (WWTP), and the results were applied to evaluate the performance of the plant. Daily average values for 209 days from the inlet and outlet of the plant obtained from WWTP documentation center along with the results of four sampling runs in this work were used for data reconciliation and performance evaluation of the plant. Results showed that standard deviation and relative errors in the balanced data of each measurement decreased, especially for the process wastewater from 24.5 to 8.6 % for flow and 24.5 to 1.5 % for chemical oxygen demand (COD). The errors of measured data were −137 m³/day (−4.41 %) and 281 kg/day (7.92 %) for flow and COD, respectively. According to the balanced data, the removal rates of COD and 5-day biological oxygen demand (BOD₅) through the aeration unit were equal to 37 and 46 %, respectively. In addition, the COD and BOD₅ concentrations were reduced by about 61.9 % (2137 kg/day) and 78.1 % (1976 kg/day), respectively, prior to the biological process. At the same time, the removal rates of benzene, toluene, and styrene were 56, 38, and 69 %, respectively. The results revealed that about 40 % of influent benzene (75.5 kg/day) is emitted to the ambient air at the overhead of the equalization basin. It can be concluded that the volatilization of organic compounds is the basic mechanism for the removal of volatile organic compounds (VOCs) and it corresponds to the main part of total COD removal from the WWTP.

     

A heuristic optimization approach for Air Quality Monitoring Network design with the simultaneous consideration of multiple pollutants

An interactive optimization methodology for allocating the number and configuration of an Air Quality Monitoring Network (AQMN) in a vast area to identify the impact of multiple pollutants is described. A mathematical model based on the multiple cell approach (MCA) was used to create monthly spatial distributions for the concentrations of the pollutants emitted from different emission sources. These spatial temporal patterns were subject to a heuristic optimization algorithm to identify the optimal configuration of a monitoring network. The objective of the optimization is to provide maximum information about multi-pollutants (i.e., CO, NO(x) and SO(2)) emitted from each source within a given area. The model was applied to a network of existing refinery stacks and the results indicate that three stations can provide a total coverage of more than 70%. In addition, the effect of the spatial correlation coefficient (R(C)) on total area coverage was analyzed. The modeling results show that as the cutoff correlation coefficient R(C) is increased from 0.75 to 0.95, the number of monitoring stations required for total coverage is increased. A high R(C) based network may not necessarily cover the entire region, but the covered region will be well represented. A low R(C) based network, on the other hand, would offer more coverage of the region, but the covered region may not be satisfactorily represented.     

Adsorption of benzene and toluene from waste gas using activated carbon activated by ZnCl2

A series of activated carbons with high surface area were prepared from walnut shell using chemical activation with ZnCl2. In this research the carbonization stage was carried out at 500℃. The performance of the synthesized carbons evaluated in adsorption of benzene and toluene from waste gas. The influence of impregnation ratio on the characteristics of synthesized activated carbons as well as their adsorption capacity was investigated. The ratio of activation agent to walnut shell was selected in the range of 0.5-2.0 wt/wt. The synthesized activated carbons were characterized using XRD, SEM, BET and FTIR techniques. The highest activated carbon production yield was obtained at impregnation ratio of 1.5 wt/wt. The XRD analysis illustrated that peaks intensity decreased with increasing impregnation ratio showing that amorphous property of samples was increased. The SEM analysis revealed successful pore development in synthesized activated carbons obtained at high impregnation ratios. The surface area of the activated carbons increased with increasing impregnation ratio and its maximum value reached 2643 m2.g 1 at impregnation ratio of 2/1. FTIR analysis indicated that the relative amount of different acidic surface groups on synthesized carbons was a function of impregnation ratio. Experimental results for benzene and toluene adsorption showed a high potential of employing synthesized impregnated activated carbon for treatment of waste gas. Generally, the amount of VOC adsorbed on the surface was affected by physicochemical properties of synthesized activated carbons.