The objective of this research is to propose the suitable suspended solid (SS) treatment process for the wastewater of the actual aquaculture systems (tilapia ponds). Sedimentation, coagulation, and depth filtration were chosen and applied in this study. Sand and anthracite were used as media in the depth filtration; while alum was used as a coagulant in jar tests. The results showed that, at the optimal operating condition, sedimentation (overflow rate of 0.8 m/hr) and coagulation (alum concentration of 15 mg/L) can provide treatment efficiencies of 90% and 99.25%, respectively. However, several drawbacks (high detention time, decrease of pH value, sludge generation) were observed. Therefore, the depth filtration processes with single and dual media were applied at different media configurations. The highest treatment efficiency (92%) and moderate filtration performance (80 minutes operating time and 12 m/hr filtration rate) can be obtained with the combination of media between anthracite (2 mm effective size and 0.15 m in depth) and sand (0.8 mm effective size and 0.55 m in depth). Finally, sedimentation as pretreatment and aeration in batch mode along the media depth were proven to significantly enhance the overall filtration performance.
Microbial fuel cell (MFC) has been receiving attention in the study field of wastewater treatment because it can recover an electrical energy directly with the treatment. In this study, MFC performance and bacterial community were investigated at different temperatures. The maximum voltage and coulombic efficiency were comparable between the MFCs using three types of ion-exchange membranes at the temperatures of 23, 28 and 33°C. However, the MFC performance with a cation-exchange membrane (CEM) was a little higher than with the two types of proton-exchange membranes (PEMs) at 28 and 33°C. The DNA band pattern on denaturing gradient gel electrophoresis (DGGE) for the biomass attached to the anode electrode varied according to the temperature and the types of membrane, however, a definite relationship between the bacterial community and the temperature was not found.
Phosphorus (P) is a limiting factor of eutrophication in many lakes. Paddy-field districts are major non-point sources of P; water pollution prevention measures are to be implemented in these districts. However, sediment in drainage canals has a large P buffering capacity and can release P to the water column when input of P from paddy fields is reduced. Therefore, it is necessary to evaluate the amounts of P in the sediment in drainage canals. In this study, the sediments in drainage canals in paddy-field districts around Lake Biwa were investigated. The amounts and fractions of P in the sediments during both the irrigation period and the non-irrigation period were analyzed. Results showed that the mean value of total P in the sediment was 0.6 g/kg in both periods, but total P in non-irrigation periods tends to be greater than that during irrigation periods for each site in the study. Furthermore, over 70% of total P was inorganic on the average. Moreover, the fractions of organic and inorganic P exhibited seasonal variability. The potential contribution of water-extractable P in the sediment to total P in drainage water increased from June to November.
The effect of the different ratios of anaerobic-aerobic time on the efficiency of enhanced biological phosphorus removal (EBPR) from synthetic wastewater with acetate as carbon source was investigated. Three pressurized pure oxygen sequencing batch reactor (POSBR) experiments were operated with a final pressure of 0.05 MPa. The reactors (POSBR1, POSBR2 and POSBR3) were developed and studied at different anaerobic-aerobic ratios of 3 : 3.5, 3 : 2.5 and 3 : 1.5, respectively. The laboratory results showed that for the polyphosphate-accumulating organisms (PAOs) more polyhydroxyalkanoates (PHAs) accumulated and phosphate was released in the anaerobic stage, while higher concentration of phosphate was taken up in the aerobic period. However, the POSBR2 had a greater phosphate release to uptake ratio than POSBR1 and POSBR3, which resulted in a much higher phosphorus removal efficiency (93.8%) than the other two operations (70.7% and 53.1%, respectively) within 30 days of operation. It was also found that POSBR2 synthesized more PHAs than others. The highest PHAs storage was observed during the anaerobic phase of POSBR2. Due to the influence of the time ratios on the PHA concentration and consumption, the condition of POSBR2 was favorable for the existence of PAO and therefore, beneficial for the biological phosphorus removal process.
There are many borrow pits caused by sand mining at the bottom of the coastal sea in Japan. Borrow pits have been identified as a source of oxygen-deficient water with hydrogen sulfide. It has become increasingly important to restore borrow pits to improve the marine environment. However, large quantities of sand materials are needed to restore borrow pits. Recently, dredged materials generated by sea route maintenance have been adopted instead of sand materials. However, one problem of dredged materials is that they can be weak ground materials. Therefore, slag-mixed material made from the dredged material and steelmaking slag has been proposed. In this study, control of hydrogen sulfide release resulting from changing the hardness of the slag-mixed materials has been examined. Hydrogen sulfide release strongly depends on the hardness of the slag-mixed material. Microbial analysis indicated fewer living bacteria and the relative abundance of sulfate-reducing bacteria in the slag-mixed material compared with the dredged material. The solidification of the dredged material using steelmaking slag decreased not only hydrogen sulfide release but also dissolved iron and manganese release. It is considered that controlling the hardness of the dredged material mixed with steelmaking slag provides an effective means of sulfide release control.
Phosphorus resources are limited in the world and there have been some alarming reports that deposits of high-grade phosphate ores are likely to be depleted in the next few decades. Layered double hydroxides (LDHs), known as hydrotalcite-like compound or anionic clays, have drawn much attention on their high adsorption capacity to various anions from aqueous solution, such as AsO43-, CrO42-, PO43-, SeO32- due to their large surface area, high anion-exchange capacities and flexible interlayer space. In this present research, a series of Mg-Fe LDHs after calcination were synthesized to adsorb phosphate from solution. The highest phosphate adsorption capacity was obtained with Mg/Fe ratio of 3 and calcined at 573 K. The adsorption kinetics which was studied by using the pseudo-second-order model showed a high adsorption capacity of 76 mg-P/g at equilibrium time of 72 h. Adsorption isotherms revealed that the phosphate uptake process was better fit to Freundlich model than Langmuir model. Distribution coefficient (Kd) revealed good adsorption selectivity to phosphate in a mixed anion solution. The adsorbed phosphate can be effectively desorbed (73%) by adding a 0.1 M NaOH solution.
The feasibility of using the photo-Fenton reaction to improve the biodegradability of non-biodegradable compounds that originated from sewage was examined. Non-biodegradable compounds are degraded by hydroxyl (OH) radicals generated by the photo-Fenton reaction. During the degradation of non-biodegradable compounds, biodegradable intermediates such as organic acids are produced, resulting in improved biodegradability. The results of an experiment, in which a filtered supernatant solution of activated sludge from a sewage treatment plant was used, confirmed that the 5-day biochemical oxygen demand (BOD5) increased with decreasing total organic carbon (TOC) concentration as a result of the photo-Fenton reaction. This increased the ratio of BOD5 to TOC, which indicated that the biodegradability was improved. Although many non-biodegradable compounds have electron-dense structures, many biodegradable compounds have electron-lucent structures. Hydroxyl radicals, which are an oxidant in the photo-Fenton reaction, act as an electrophilic agent. In the degradation experiments using a mixture of biodegradable and non-biodegradable compounds, OH radicals preferentially attacked non-biodegradable compounds, and biodegradable compounds accumulated in the solution. As a result, the biodegradability was improved.