A Material Transformation Model for Biological Stabilization Ponds
Biological stabilization ponds have been accepted as an effective and economical means of waste water treatment and have been applied for many years throughout the world. This is one kind of semi-natural ecosystem in which various material transformation
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AMaterial Transformation Model for Biological Stabilization Ponds Xianghua Wen
Introduction
B
iological stabilization ponds have been accepted as an effective and economical means of waste water treatment and have been applied for many years throughout the world. This is one kind of semi-natural ecosystem in which various material transformation processes take place. Among these processes, carbon, nitrogen and phosphorus transformations are the most important ones. From an ecological point of view, material transformation and cycling processes are crucial for keeping the system stable.' Some researchers Ho have discovered the importance of material transformation in biological stabilization ponds. However, systematic and quantitative studies of nutrient transformation processes by applying the principles of ecology are few and insufficient. The objective of this chapter is to establish a good model of material transformation in biological stabilization pond systems based upon principles of ecology. This model shall completely describe the transformation processes of carbon, nitrogen and phosphorus in a pond system. In an application of the model, it was successfully used in making material transformation graphics for visual and quantitative analysis of material transformation processes in biological stabilization pond systems. As a result, a better and more comprehensive understanding of pond mechanisms can be achieved. This model is also very reliable for pond design and operational control. Furthermore, these study procedures are uniquely complete in terms of systematization of the designs for the experiments, as well as model calibration and verification.
Model Development Modeling techniques are a very effective means to analyze a complex system, because modeling can clearly demonstrate the properties of the system and remedy deficiencies in our knowledge. Mass conservation is the most basic law of
Wastewater Treatment with Algae, edited by Yuk-Shan Wong and Nora F.Y. Tam. Springer - Verlag and Landes Bioscience 1998.
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Wastewater Treatment with Algae
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ecology. Our model is based on this law and the hypothesis of a completely mixed flow in the pond. The mathematical description of the above mentioned items is Equation 1. de dt
=QC
j -
Q"C+ V
• .feVe)
j
1)
Where: Cj, C influent and effluent concentration of substance, respectively (mg/l); dc/dt change rate of substance in pond (mg/l.d) V pond volume (1); Q, Qe influent and effluent flow rate, respectively (lid); n number of reactions that involve the substance Material transformation processes in biological stabilization pond systems are very complicated. It is impossible to simulate all the details of their transformation processes, even only for carbon, nitrogen and phosphorus. We have made some assumptions in order to develop a proper model. For carbon, as shown in Figure 11.1 we assume that it exists in four forms: 1) Dissolved inorganic carbon(CI); 2) Carbon content of bacterial cells (C B); 3) Dissolved organic carbon (Co); and 4) C
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