A dissertation submitted in partial fulfillment of the requirements for the degree of Doctoral of Technical Science, School of Environment, Resources and Development

Laboratory experiments, a survey and {uFB01}eld experiment were conducted to explore the potential of the oyster Crassosrrea belcheri as a bio{uFB01}lter system and wastewater treatment in intensive shrimp culture. A series of laboratory experiments were conducted to examine the effect of water salinity on the {uFB01}ltration rate of oysters, the performance of oyster feeding on phytoplankton commonly found in intensive shrimp ponds, characteristics of suspended solid particles in shrimp pond water, and the effects of using a settling tank on nutrient removal and feeding performance of oysters. The survey examined the species composition and density of the dominant phytoplankton species in intensive shrimp pond water. The {uFB01}eld experiment examined the effect of water {uFB02}ow rate on oysters feeding on shrimp pond water in a real shrimp pond environment. The results obtained from those experiments were used to develop the basic design parameters for a treatment system, and its performance was assessed. Over a salinity range of 10-35 ppt, maximum {uFB01}ltration rates were obtained with salinities between 10 and 25 ppt for both small and large size oysters. The average {uFB01}ltration rates of both sizes of oyster were found to be highly correlated with water salinity. In a survey of 20 intensive shrimp ponds sampled throughout the culture period, 47 species of phytoplankton were identi{uFB01}ed. Dominant species and species composition was related to salinity. One group was typically found associated with salinity 10-30 ppt, and included as dominant species blue green algae Oscillatoria perornara, Chroococcus minatus and Microcystis aeruginosa; green alga Oocystis elliptica; diatoms Coscinodiscus sp. and Niztschia closrerium; and dinoflagelates Protoperidinium divergents and Gymnodinium dissimiles. The group associated with salinities >31 ppt was dominated by similar species but with different densities. The dominant species were blue green algae Oscillaioria. lemmermannii, Chorococcus minatus and Microcystis aeruginosa; green alga Oocystis elliprica; diatoms Coscinodiscus sp. and Niztschia closterium and dino{uFB02}agelates Protoperidinium divergents, Gymnodinium dissimiles and Prorocentrum micans. Different concentrations of ammonia in shrimp pond water had an effect on the dominant species of phytoplankton. When ammonia-N concentrations were $0.19 mg 1" , more than 77% of total the phytoplankton density was composed of two species, Osillatoria lemm_e mann1'i and Oocystis elliplica. When the ammonia-N concentrations were >1.9 mg l , 70% of the phytoplankton was one species, O. lemmermannii. Four trials were conducted to examine the performance of oysters feeding on phytoplankton commonly found in intensive shrimp ponds. The pond water consisted mainly of Oscillatoria lemmermannii (trial l), Protoperidinium divergents and O. lemmermannii (trial 2), Oocystis elliptica (trial 3) and O. perornata (trial 4). The oysters fed on shrimp pond water with different dominant species of phytoplankton were found to vary in {uFB01}ltration rate, assimilation ef{uFB01}ciency and biodeposition rate. The phytoplankton composition of the shrimp pond water differed greatly from that of the stomach contents. A smaller size of phytoplankton was always found in the oyster stomachs that in the corresponding shrimp ponds, while phytoplankton of a larger size were predominant in the matter ejected as pseudofaeces. Settling velocities of particulate solids in shrimp pond water at a culture period of 39, 86 days, and at harvest were 0.03, 0.04 and 0.03 cm.sec'l, respectively. Removal rates of 40-60% over the production cycle were achieved at over{uFB02}ow rates of 10.1-22.6 m3m'2d{u2019}l. The majority of the particles in the culture water were found to be smaller than 16 pm. Total N and total P in shrimp pond water from different culture periods were reduced after standing quiescent for a period of time. Increasing the standing time beyond 30 min did not lead to further signi{uFB01}cant reductions. Use of a settling tank did not enhance the {uFB01}ltration rate and assimilation efficiency of oysters, but did reduce the biodeposition rate. Mean filtration rates of oysters were not signi{uFB01}cantly different at water velocities above 0.077 cm.sec". Assimilation efficiency was slightly increased by increasing the water velocities. Biodeposition rates increased when the water velocity increased above 0.108 cm sec". The total suspended solids, total N and total P removed and nutrients regenerated by the oysters in the experimental system, including ammonia-N, nitrite, nitrate, and orthophosphate were related to water velocities. A basic design and operation assumed 1 ha shrimp pond of 1.5 m depth with regular water exchange of 40% per day. The treatment unit required 414 m for the sedimentation unit, and 466 m2 for the oyster unit (125 oysters m'2 of 5-7 cm shell length). Pumping rates of 4,166 m3 mind were required to maintain a water {uFB02}ow per unit surface area of the sedimentation unit at around 14.5 m3m'2d" and a water velocity in the oyster unit at the rate of 0.185 cm sec". Under a basic design, it was estimated that a settling pond removed 50% of total suspended solids, 23.9% of total N and 17.7% oftotal P, while the oysters removed 21% oftotal suspended solids, 9% of total N and 6% of total P. There was an estimated increased discharge of only about 2.7% of ammonia-N, 10.1% of nitrite, 4.6% of nitrate, and 0.2% of orthophosphate.

Thesis (Ph.D.) - Asian Institute of Technology, 2001