The biodegradation of linear alkylbenzene sulfonate (LAS) was examined in several habitats of a laundromat wastewater pond and pristine control pond. Biodegradation was determined by measuring evolution over time of ¹⁴CO₂ from a trace level (50 ppb) of ¹⁴C-ring LAS added to samples obtained from the pond. Habitats investigated included pondwater, sediments, decaying plant detritus, cattail rhizosphere, duckweed phylloplane, floating cyanobacterial mat, topsoil, saturated and unsaturated subsurface soils and groundwater. In the wastewater pond, the highest biodegradative activity was associated with detritus, cattail rhizosphere, algal-bacterial mat, saturated subsoil beneath the pond and nearby topsoil. In the control pond, LAS was degraded in aerobic sediments, cattail rhizosphere, detritus and saturated subsoil immediately beneath the pond. Generally, biodegradative activity in wastewater pond habitats was higher than in corresponding control pond habitats. Key factors affecting distribution of degradative activity were LAS exposure and redox potential. This study shows that LAS degradation occurs in a wide range of environmental compartments and is higher in systems with a history of exposure.

View full abstract

This paper presented the conditions of oxygen supply which enabled the simultaneous denitrification with nitrification in full-scale oxidation ditches.
Oxygenation capacity (OC) per organic load ratio was introduced as an important control parameter for the simultaneous removal of organic substances and nitrogen compounds. This OC/organic load ratio has been used as a “rule of thumb” to calculate the required oxygen supply.
Above OC/COD_cr load of 0.75kgO₂·kg^-1COD_cr, 80-95% COD_cr removal was obtained in full-scale oxidation ditches. At OC/COD_cr load ratio above 1.0kgO₂·kg^-1COD_cr, the sufficient nitrification was achieved, but below this value the nitrification rate decreased rapidly. On the other hand, the denitrification efficiency was more than 90% below 1.3kgO₂·kg^-1COD_cr of OC/COD_cr load, although the denitrification rate decreased with increasing OC/COD_cr load. Consequently, optimum OC/COD_cr load ratio for the nitrogen removal existed from 1.0 to 1.3kgO₂/ kgCOD_cr, which corresponded to 1.4-1.9kgO₂·kg^-1BOD₅ in OC/BOD load.
Operation with the simultaneous removal of organic substances and nitrogen compounds in oxidation ditches reduced the amount of oxygen supply by approximately 20%, compared with operation without denitrification. Hence, the removal of organic substances by the denitrification reduced to a considerable extent, the energy demand of aeration.

View full abstract

The fixed bed submerged filtration is known to take long time to form biofilm on the support media. Purpose of present study is to improve this problem by introducing a quick biofilm forming method described as follows. Activated sludge supplemented with ferromagnetic powder (magnetic activated sludge) was attracted on sheets of plastic magnet support media by magnetic force to form biofilm.
The method reduced time needed only several minutes for the formation of biofilm. Forty three g·m^-2 biomass were attracted on the magnet support media by immersing into suspension of magnetic activated sludge. This biofilm was found to remove 80-85% COD from the synthetic waste water (a COD loading of 5.5 g·m^-2d^-1). The biofilm was not detached from the support media during the experimental period.
The synthetic wastewater was treated sufficiently from the the start-up without increase of biomass in the biofilm. These results suggest that this method is more efficient than usual method.

View full abstract

The purpose of this reserch was to develop a calcium phosphate crystallization method to remove phosphate from wastewater. The efficiency of phosphorus removal with the contact media prepared from coral reef limestone, phosphate rock or activated alumina was studied by column tests.
A phenomenon was observed that phosphorus removal ability of the coral reef limestone increased as the column test continued. It was found that hydroxyapatite crystals: Ca₅(PO₄)₃ (OH) were formed on the surface of the coral reef limestone and the BET-surface area of the coral reef limestone was increased.
From these results, it was suggested that efficiency of phosphorus removal was affected by the crystallization phenomena on the coral reef limestone. It was shown that phosphate in the feed solution was reduced to a low level by the crystallization method using coral reef limestone as seed materials and the performance of a stability was achieved during 50 days of continuous column test operation.

View full abstract

Intermittently aerated activated sludge system has the flexibility against variations of inflow, because aerobic and anaerobic periods can be determined in time base. And also it can be applied to existing activated sludge processes by minor structual changes. This paper show the design and control strategies of intermittently aerated activated sludge process, which give the simultaneous and stable removal of nitrogen and phosphorus.
In a reconstructed extended aeration plant (design capacity 625m³·d^-1), under the condition of F/M ratio 0.022-0.037 (kgBOD₅·kg^-1MLSS) and N/M ratio 0.0064-0.0092 (kgT-N·kg^-1MLSS), the effluent quality was kept less than T-N 5mg·l^-1 and T-P 1mg·l^-1 during a year. In a more advanced control period, the average values of total nitrogen and total phosphorus were 1.8mg·l^-1 and 0.2mg·l^-1. Dynamics of nitrogen and phosphorus in the reaction basin along the flow are shown in the paper.
It is shown that two stage structure of reaction basin is primarily important, and next the control strategies which guarantee the first basin to pass through a deep anoxic condition and the last basin to be kept in an oxic condition is necessary.

View full abstract