AMMONIA ELIMINATION PROCESSES IN STABILIZATION AND HIGH-RATE ALGAL POND SYSTEMS

Stabilisation pond (SP) and high-rate algal pond (HRAP) wastewater tre atment systems are based on the same processes, but differ in their ca pacity to remove ammonia. This study analyzes the processes concerning ammonia elimination. The different factors studied are: (i) light irr adiance and temperature, (ii) phytoplankton uptake, and (iii) chemical characteristics affecting ammonia concentration. The variables releva nt to these processes have been used in path analysis studies. Differe nt variables describing the studied processes have been used to quanti fy the different phenomena. A conceptual model has been developed, and applied to each pond. Path analysis technique has been applied. it is a causal modelling technique. The evaluation of causal models involve s theoretical, methodological and statistical analysis. Theoretical co nsiderations have been defined in the list of the processes studied. M ethodological considerations involve the variable measurements on a de fined time-scale. The statistical aspect consists of the evaluation of structural equation models. The results of these studies show that th e principal phenomena affecting ammonia in SP systems are temperature, pH, and total nitrogen input. In HRAP systems ammonia variability is directly linked to pH, temperature, nitrite and total nitrogen input, and indirectly linked to chlorophyll a concentration and pH. The perce ntage of observed variability given by the models (R(2) = coefficient of determination) ranges between 46% and 60.8%.