Energy saving processes for nitrogen removal in organic wastewater from food processing industries in Thailand.

Nitrogen removal from organic wastewater is becoming a demand in developed communities. The use of nitrite as intermediate in the treatment of wastewater has been largely ignored, but is actually a relevant energy saving process compared to conventional nitrification/denitrification using nitrate as intermediate. Full-scale results and pilot-scale results using this process are presented. The process needs some additional process considerations and process control to be utilized. Especially under tropical conditions the nitritation process will round easily, and it must be expected that many AS treatment plants in the food industry already produce NO2-N. This uncontrolled nitrogen conversion can be the main cause for sludge bulking problems. It is expected that sludge bulking problems in many cases can be solved just by changing the process control in order to run a more consequent nitritation. Theoretically this process will decrease the oxygen consumption for oxidation by 25% and the use of carbon source for the reduction will be decreased by 40% compared to the conventional process.

Removal of indicator bacteria from municipal wastewater in an experimental two-stage vertical flow constructed wetland system.

The removal of sanitary indicator bacteria (total coliforms, faecal coliforms, and faecal streptococci) was studied in an experimental constructed wetland system consisting of (1) a 2-m3 three-chamber sedimentation tank, (2) a 5 m2 vertical flow constructed wetland, (3) a filter-unit with calcite aimed at removing phosphorus, and (4) a 10 m2 vertical flow constructed wetland. The indicator bacteria were enumerated before and after each unit of the wetland system during four monitoring episodes with different loading conditions. At a hydraulic loading rate of 520-1,370 mm/d, the first-stage vertical flow beds removed about 1.5 log-units of total coliforms, 1.7 log-units of faecal coliforms and 0.8 log-units of faecal streptococci. In the second stage bed receiving lower loadings both in term of concentration and quantity (260-690 mm/day), the eliminations were lower. It was not possible in the present study to identify any seasonal effects, but no measurements were done during summer. Recycling of treated effluent back to the sedimentation tank did not affect elimination. Area-based rate constants for the vertical flow wetland receiving effluent from the sedimentation tank averaged 3.2 m/d for total coliforms, 3.3 m/d for faecal coliforms and 2.1 m/d for faecal streptococci. The rate constants depended on loading rates. It is suggested that filtration is a major removal mechanism for bacterial indicator organisms in vertical flow constructed wetland systems.

Phosphorus removal from municipal wastewater in an experimental two-stage vertical flow constructed wetland system equipped with a calcite filter.

Laboratory studies have indicated that calcite may be used in separate, exchangeable filter units in constructed wetland systems to remove phosphorus. Based on these studies we built a full-scale experimental constructed wetland with a calcite-based filter unit to study its performance, under real-life conditions. The system consists of a 2-m3 sedimentation tank and two vertical flow constructed wetlands. The system has three 0.09 m3 calcite filter-units to study phosphorus removal. The hydraulic loading rate varied between 1.7 and 6.2 m3/d. The residence time in filters ranged from 28 to 99 minutes. Overall the system removed 62 +/- 18% of phosphorus. The removal in the calcite filter was initially good, but after three months all P-filters were saturated. The calcite increased pH by approximately half a unit and released calcium. A total of about 2.2 kg P/m3 calcite was removed by the filter. The first-stage bed receiving effluent from the sedimentation tank consistently removed phosphorus, whereas the second bed sometimes released phosphorus. The first order area-based removal rate constant for total-P in the vertical bed averaged 0.24 +/- 0.20 m/d and was highly dependent on the loading rate. This shows that first order removal kinetics do not satisfactorily describe removal of phosphorus in vertical flow constructed wetland systems with unsaturated flow.