ECOLOGICAL STUDIES OF WASTE STABILISATION PONDS

Abstract

Waste stabilization ponds, with its bio tic-abiotic component and the habitat forms a complete ecological system, •wherein the populations are interacting, interaffecting and interdependent. The criteria of design for these ponds 3(nJ) based on semi-rational approach and experience. le existing mathematical models, to explain the function ing of these ponds are mostly individualistic, describing some aspect of pond phenomenon. Even the models which have ventured beyond the classical BOD approach and have consi dered complex bio-geo chemical transformations within the pond, suffer from eertain limitations. In these ponds the significance of functional ecologi cal parameters viz., production (P) and respiration (R) which are indicative of synthesis and utilization have been established. The effect of growth promoting factors on pond performance and eeological parameters have been studied on Laboratory G.I. pond aquaria under natural conditions. Using optimal Carbon, Nitrogen, Phosphorous (C«N:P) ratios* at varying organic loads, P/R ratio points out clearly towards a more rational approach to design criteria. It distinctly adds greater dimension to the understanding of the pond phenomenon - significantly different from the classical BOD approach and encompassing a more comprehensive definition of the complexities of the ecosystem. With the experimental information thus generated, system equations have been established as a set of first order total differential equations relating state variables to input variables. The parameters so involved in the system equations describe the behaviour of the system in totality. Knowing the initial state of the system its future state can be predicted for known inputs. As a special case the state of the system, undergoing stresses due to organic load, can also be predicted after the stresses have been relieved. The state model thus developed has been validated on a pilot plant. The investigations clearly showed a distinct orienta tion to a new approach to pond design and operation i.e. as an optimisation problem with time varying constraints and optimal control problems, respectively.