Title: Ultimate biochemical oxygen demand in semi-intensively managed shrimp pond waters Authors
|Ward, George -|
Submitted to: Aquaculture
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: June 21, 2011
Publication Date: August 11, 2011
Citation: Green, B.W., Ward, G.H. 2011. Ultimate biochemical oxygen demand in semi-intensively managed shrimp pond waters. Aquaculture. 319:253-261. Interpretive Summary: Pond water and effluent contain a varied mixture of mineral and organic byproducts, including organic carbon compounds, inorganic and organic forms of nitrogen, phosphorus, and silicon, both in suspension and solution, as well as a variety of microorganisms. Some of these constituents exert a direct effect on dissolved oxygen consumption through chemical reactions, respiration, or degradation of complex organics by aerobic and facultative bacteria, while others have an indirect effect on dissolved oxygen by stimulating the growth of algae or aquatic organisms in the receiving waters. One measure of microbiological respiration is the biochemical oxygen demand (BOD), which measures the oxygen consumed in a specified time period per unit volume of water, in the absence of photosynthesis. Dissolved oxygen consumption over time increases rapidly at first then approaches an asymptotic value. This asymptote, termed the ultimate BOD, denoted UBOD, is conceived to be the maximum potential oxygen demand from the readily degradable components of the sample. In three independent studies, the ultimate biochemical oxygen demand was measured in waters and effluents from marine shrimp production ponds on six shrimp farms in Honduras during the rainy and dry seasons. Organic matter in pond water was almost completely degraded after 30 days during the dry season, whereas during the rainy season nearly 90 days were required because of the higher biomass of phytoplankton. A 5-day biochemical oxygen demand less than 30 mg/L dissolved oxygen is used as a standard for pond effluent. All pond water and effluent samples measured in this work had a 5-day BOD less than this standard.
Technical Abstract: Three independent studies were conducted to quantified ultimate biochemical oxygen demand (UBOD) and the corresponding decomposition rate constant for production pond (average 21.5 ha each) waters and effluents on six semi-intensively managed marine shrimp (Litopenaeus vannamei) farms in Honduras. Samples were collected during the rainy season in studies 1-3 and during the dry season only in study 1. The dry season 30-d biochemical oxygen demand (BOD30) of pond waters across all farms was 26% lower and UBOD was 54% lower, but the decomposition rate constant was more than twice as great as during the rainy season. During the dry season, biochemical oxygen demand was nearly completely expressed after 30 d of incubation whereas during the rainy season BOD was about 65% expressed after 31 d of incubation and the correlation between BOD31 and UBOD was less strong compared to the dry season. Water quality variables were correlated with measures of BOD during rainy and dry seasons, but only the correlation between chlorophyll a and BOD measures was predictive. In studies 2 and 3, BOD after 88-94 d of incubation was expressed almost completely and corresponded closely with predicted UBOD. All pond water and effluent samples had a BOD5 concentration less than 30 mg/L.