Sorawit Powtongsook

Water quality control using Spirulina platensis in shrimp culture tanks

A cyanobacterium (Spirulina platensis) was co-cultured with black tiger shrimp (Penaeus monodon) for water quality control. We evaluated the effects of: (1) three S. platensis trial conditions on inorganic nitrogen concentrations at one shrimp density (S. platensis trial conditions included: absent, nonharvested and semicontinuous harvesting) and (2) two shrimp densities on inorganic nitrogen concentrations, with and without S. platensis. Semicontinuous harvesting of S. platensis at one shrimp density resulted in significantly reduced (P<0.05) inorganic nitrogen concentrations (NH4, NO2 and NO3). With S. platensis absent, ammonium and nitrite concentrations ranged from 0.5 to 0.6 mg l−1, while nitrate concentrations ranged from 16 to 18 mg l−1 by day 44. With nonharvested S. platensis, considerable variability occurred with nitrogen concentrations. Semicontinuous harvest of S. platensis reduced nitrate to 4 mg l−1, while ammonium and nitrite ranged from 0.0 to 0.15 mg l−1, respectively. The factorial evaluation of shrimp density versus presence and absence of S. platensis resulted in greatly reduced nitrogenous compounds with S. platensis present regardless of shrimp density, and only moderately increased nitrogen with greater shrimp density. Without S. platensis, all nitrogen compounds were substantially elevated and shrimp survived was significantly reduced at high shrimp density.

Flat panel airlift photobioreactors for cultivation of vegetative cells of microalga Haematococcus pluvialis

The novel flat panel airlift photobioreactor (FP-ALPBR) was proposed as an alternative system for the cultivation of Haematococcus pluvialis NIES-144. Changes in the efficiency of the system were tested in response to variations in two engineering parameters: the ratio between the downcomer and riser cross-sectional areas (A(d)/A(r)) and the size of the system (as determined by the length of the panel) and to one operating parameter: the superficial gas velocity (u(sg)). The best growth performance was obtained by operating the system at a superficial velocity of 0.4 cms(-1) and with a downcomer-to-riser cross-sectional area ratio of 0.4. The 17-l FP-ALPBR system was capable of giving reasonable growth characteristics with a maximum cell density of 4.1 x 10(5)cell ml(-1) and specific growth rate of 0.52 day(-1) being achieved. A similar level of performance was obtained from the 90-l FP-ALPBR system, i.e., cell density=40 x 10(4)cell ml(-1) but with a slight decrease in specific growth rate to 0.39 day(-1). The performances of these two differently sized FP-ALPBRs were compared with two conventional cylindrical airlift photobioreactors (C-ALPBRs) of different dimensions. The 90-l FP-ALPBR exhibited reasonably good performance when compared with the two 17-l systems (both C- and FP-ALPBRs); however, the best growth rate was observed using the 3-l C-ALPBR. Semi-continuous cultures, which could be periodically harvested at a reasonably high growth rate, were successfully created. Of all the systems investigated in this study, the 90-l FP-ALPBR was found to be the most cost-effective, as it could cultivate 18 g of alga for approximately US

Airlift bioreactor containing chitosan-immobilized Sphingobium sp. P2 for treatment of lubricants in wastewater.

21.

Inorganic nitrogen control in a novel zero-water exchanged aquaculture system integrated with airlift-submerged fibrous nitrifying biofilters

An internal loop airlift bioreactor containing chitosan-immobilized Sphingobium sp. P2 was applied for the removal of automotive lubricants from emulsified wastewater. The chitosan-immobilized bacteria had higher lubricant removal efficiency than free and killed-immobilized cells because they were able to sorp and degrade the lubricants simultaneously. In a semi-continuous batch experiment, the immobilized bacteria were able to remove 80-90% of the 200 mg L(-1) total petroleum hydrocarbons (TPH) from both synthetic and carwash wastewater. The internal loop airlift bioreactor, containing 4 g L(-1) immobilized bacteria, was later designed and operated at 2.0 h HRT (hydraulic retention time) for over 70 days. At a steady state, the reactor continuously removed 85±5% TPH and 73±11% chemical oxygen demand (COD) from the carwash wastewater with 25-200 mg L(-1) amended lubricant. The internal loop airlift reactors simple operation and high stability demonstrate its high potential for use in treating lubricants in emulsified wastewater from carwashes and other industries.

Immobilization of nitrite oxidizing bacteria using biopolymeric chitosan media

This work examined the feasibility of applying shrimp diets to establish nitrification on submerged fibrous biofilters. It also investigated the performance of a proposed zero-water exchanged aquaculture system, which integrated growing of aquatic stocks and operation of acclimated biofilters in the same environment. Addition of shrimp diets fully established nitrification within 3 weeks as indicated by continuous increase of nitrate and trivial levels of ammonium and nitrite. A series of batch experiment revealed an average ammonium degradation rate of 24.1mg Nm(-2) day(-1). Zero-water discharged tilapia cultivation could be carried out in the proposed aquaculture system for at least 44 days when daily inorganic loadings increased from 1.24 to 10.78mg Nl(-1) day(-1). The corresponding daily growth rates of tilapia from the proposed aquaculture systems integrated with acclimated biofilters varied from 3.01 to 3.35g day(-1), which was approximately 7-16% better than numbers from the systems using non-acclimated biofilters.

Communities of ammonia-oxidizing bacteria, ammonia-oxidizing archaea and nitrite-oxidizing bacteria in shrimp ponds

The effects of chitosan characteristics including the degree of deacetylation, molecular weight, particle size, pH pretreatment and immobilization time on the immobilization of nitrite-oxidizing bacteria (NOB) on biopolymeric chitosan were investigated. Nitrite removal efficiency of immobilized NOB depended on the degree of deacetylation, particle size, pH pretreatment on the surface of chitosan and immobilization time. Scanning electron microscope characterization illustrated that the number of NOB cells attached to the surface of chitosan increased with an increment of immobilization time. The optimal condition for NOB immobilization on chitosan was achieved during a 24-hr immobilization period using chitosan with the degree of deacetylation larger than 80% and various particle size ranges between 1-5 mm at pH 6.5. In general, the NOB immobilized on chitosan flakes has a high potential to remove excess nitrite from wastewater and aquaculture systems.

Optimization and evaluation of a bottom substrate denitrification tank for nitrate removal from a recirculating aquaculture system

The communities of nitrifying microorganisms were identified in samples taken from six shrimp ponds in Thailand (five outdoor-earthen ponds and one indoor pond). The sequences of ammonia-oxidizing bacteria (AOB), ammonia-oxidizing archaea (AOA), and nitrite-oxidizing bacteria (NOB) were analyzed after specific PCR amplification of the 16S rRNA or amoA genes. Among the ammonia-oxidizing microorganisms, AOB appeared to be the most dispersed throughout the ponds, while AOA sequences were only retrieved from three ponds. The AOB found in the shrimp ponds belonged to only two AOB clusters, the Nitrosomonas sp. Nm143 cluster and Nitrosomonas marina cluster, which are reported with salt requirements. The majority of AOA sequences fell closer to group I.1a Thaumarcheota rather than group I.1b Thaumarcheota. For NOB, Nitrospira, but not Nitrobacter, were detected. NOB of sublineage II and IV Nitrospira, which were previously reported as salt tolerant and salt requirement NOB, were found to be common in the shrimp ponds. Insight into ammonia-oxidizing microorganisms, numbers of AOB and AOA amoA genes in two selected ponds (one outdoor-earthen ponds and one indoor pond) were quantified using qPCR. High numbers of AOA amoA genes were found in both ponds. The information obtained from this study clearly identifies the microorganisms responsible for nitrification in shrimp ponds.

Nitrogen compounds removal in a packed bed external loop airlift bioreactor

A bottom substrate denitrification tank for a recirculating aquaculture system was developed. The laboratory scale denitrification tank was an 8 L tank (0.04 m2 tank surface area), packed to a depth of 5 cm with a bottom substrate for natural denitrifying bacteria. An aquarium pump was used for gentle water mixing in the tank; the dissolved oxygen in the water was maintained in aerobic conditions (e.g. > 2 mg/L) while anoxic conditions predominated only at the bottom substrate layer. The results showed that, among the four substrates tested (soil, sand, pumice stone and vermiculite), pumice was the most preferable material. Comparing carbon supplementation using methanol and molasses, methanol was chosen as the carbon source because it provided a higher denitrification rate than molasses. When methanol was applied at the optimal COD:N ratio of 5:1, a nitrate removal rate of 4591 +/- 133 mg-N/m2 tank bottom area/day was achieved. Finally, nitrate removal using an 80 L denitrification tank was evaluated with a 610 L recirculating tilapia culture system. Nitrate treatment was performed by batch transferring high nitrate water from the nitrification tank into the denitrification tank and mixing with methanol at a COD:N ratio of 5:1. The results from five batches of nitrate treatment revealed that nitrate was successfully removed from water without the accumulation of nitrite and ammonia. The average nitrate removal efficiency was 85.17% and the average denitrification rate of the denitrification tank was 6311 +/- 945 mg-N/m2 tank bottom area/day or 126 +/- 18 mg-N/L of pumice packing volume/day.

Differences in nitrite-oxidizing communities and kinetics in a brackish environment after enrichment at low and high nitrite concentrations

A packed bed external loop airlift bioreactor (PBELAB) was proposed as an alternative treatment system for wastewater containing ammonia and nitrate compounds. The 60L PBELAB consisted of aeration and non-aeration zones, both of which were packed with plastic bioballs to enhance the surface area for the attachment of bacteria. The system was able to achieve complete removal of all nitrogen compounds with simultaneous nitrification and denitrification, i.e., ammonia was decomposed in the aeration zone and nitrate was biodegraded in the non-aeration zone. At normal operation, the nitrification rate obtained from the system was in the range of 0.14-0.87 gNH3-N/m2d and the denitrification rate was 0.04 gNO3-N/m2d. The factors found to have great influence on the system included dissolved oxygen concentration and biofilm thickness. In addition, PBELAB was proven to perform well under nitrate shock load condition.

Biomass and lipid enhancement in Ankistrodesmus sp. cultured with reused and minimal nutrients media.

Nitrite accumulation in shrimp ponds can pose serious adverse effects to shrimp production and the environment. This study aims to develop an effective process for the enrichment of ready-to-use nitrite-oxidizing bacteria (NOB) inocula that would be appropriate for nitrite removal in brackish shrimp ponds. To achieve this objective, the effects of nitrite concentrations on NOB communities and nitrite oxidation kinetics in a brackish environment were investigated. Moving-bed biofilm sequencing batch reactors and continuous moving-bed biofilm reactors were used for the enrichment of NOB at various nitrite concentrations, using sediment from brackish shrimp ponds as seed inoculum. The results from NOB population analysis with quantitative polymerase chain reaction (qPCR) show that only Nitrospira were detected in the sediment from the shrimp ponds. After the enrichment, both Nitrospira and Nitrobacter coexisted in the reactors controlling effluent nitrite at 0.1 and 0.5 mg-NO2(-)-N/L. On the other hand, in the reactors controlling effluent nitrite at 3, 20, and 100 mg-NO2(-)-N/L, Nitrobacter outcompeted Nitrospira in many orders of magnitude. The half saturation coefficients (Ks) for nitrite oxidation of the enrichments at low nitrite concentrations (0.1 and 0.5 mg-NO2(-)-N/L) were in the range of 0.71-0.98 mg-NO2(-)-N/L. In contrast, the K(s) values of NOB enriched at high nitrite concentrations (3, 20, and 100 mg-NO2(-)-N/L) were much higher (8.36-12.20 mg-NO2(-)-N/L). The results suggest that the selection of nitrite concentrations for the enrichment of NOB inocula can significantly influence NOB populations and kinetics, which could affect the effectiveness of their applications in brackish shrimp ponds.