I. Introduction
During the recent decades, environmental researches related to wastewater treatment plant have become popular due to rising concern. The developments in modeling methods make them possible to use complex system. Because of the complex system, the performance of digesters under changing organic loading rates is unpredictable [1]. Several successful models have been published for waste water treatment plants (WWTP) [2]–[5]. These models are about forecasting WWTP effluent parameters properties, process control of WWTP, predictions of WWTP parameters. Some of the parameters used for the model validation were temperature, total suspended solids (TSS), pH, chemical oxygen demand (COD), biogas production, Biological Oxygen Demand (BOD) and volatile solids. Unsuitable operation of a WWTP may cause to happen disquieting problem such as environmental and public health. Its effluent to a receiving water body can cause a broad spectrum disease to human beings. To control of a WWTP for predict the WWTP performance, the robust models can be developed using past observation data. [6].