Ammonia variations in phytotreatment ponds of land-based fish farm wastewater

The present study reports the results of 2 years monitoring of ammonia present in intensive seafarm water and in the effluent from phytotreatment ponds (lagooning) to which fish farm wastewater is conveyed before discharge into the Orbetello Lagoon (Tuscany, Italy). The aims were: (1) to evaluate the quality of the water discharged into the receiving environment, which consists of a shallow coastal lagoon with low renewal rate; (2) to assess the effect of lagooning on fish farming wastewater with reference to total ammonia and undissociated ammonia. During the test period, physicochemical parameters were measured using two HYDROLAB Datasonde 3 multiparameter probes. Water samples were taken monthly. Ammonia determinations were performed on a BRAN + LUEBBE AA III Autoanalyzer. Recorded undissociated ammonia concentrations represent a critical water quality element for the receiving environment: the NH3 during the above period lay between 0.16 and 5.06 muM (annual mean: 1.12 +/- 1.21 muM). The increase in pH occurring inside the system appreciably increases undissociated ammonia content as a result of high macroalgal development. The pH pick value (8.56 unity) was recorded in the treatment ponds in October. Undissociated ammonia increases wastewater toxicity, but, at the same time, its volatilization is an important mechanism of nitrogen removal, which reduces the eutrophizing contribution of the wastewater itself. (C) 2003 Elsevier Science B.V. All rights reserved.