Assessment of Wastewater Treatment Plant Performance using Capability Indices

Abstract

In usual practice, performance of wastewater treatment plant is assessed by percentage removal of Chemical Oxygen Demand (COD), Biochemical Oxygen Demand (BOD) and Total Suspended Solids (TSS) from wastewater after processing. Besides these, while measuring performance of wastewater plant environmental engineers also expect to consider the status of characteristics such as pH, NH4-N, N-Total, fecal coliform, etc at outlet. The problem with usual practice of performance assessment is that there is no direct comparison between these characteristics process distribution at outlet stage and effluent discharged standards or specification limits developed by Central Pollution Control Board (CPCB) for these characteristics. Considering this lacuna in mind, in this paper we propose and use probability based Process Capability Indices (PCIs) and Multivariate Process Capability Indices (MPCIs) which compares the output of wastewater treatment process with the process specifications and quantify how well the process performs. PCIs have been widely used in evaluating the performance of manufacturing processes and used as a basis to improve the process performance. From an environmental engineer's point of view, the intention of this paper is to extend applications of PCIs and MPCIs in the field of environmental engineering. Measuring wastewater treatment process performance using capability indices effectively and then process improvement based on these indices is necessary to save the environment and enable reuse of processed water. The wastewater treatment process capability analysis using appropriate capability indices is presented in the paper based on secondary data which is collected from case studies through literature survey. It is found that using appropriate capability indices, wastewater treatment processes performance can be assessed effectively as compared to usual practice.