Abstract
Onsite application of oxygen supply in domestic wastewater system may be influenced by several factors that can inhibit the oxidation and nitrification processes. In this study, the influence of aeration rate on the Johkasou performance was focused using two Johkasou facilities serving up to five persons household. In the Johkasou A (JO-A) system, we increased the aeration rate from 30 to 63 L.min-1 whereas, in the Johkasou B (JO-B), it was decreased from 59 to 34 L.min-1. Water and sludge samples were collected from the anaerobic-anoxic-oxic zones before and after adjustment of the aeration rate measured for organic matters and nitrogen parameters. Increasing the aeration rate in JO-A resulted in a high removal of organic matter (82.5%) and nitrogen (60.3%) compared to decreasing of aeration rate in JO-B (52.0% and 33.0%, respectively). Simultaneous nitrification and denitrification (SND) exhibited a maximum percentage when the aeration rate was increased compared to decreasing of aeration rate. These results indicate that application of a high aeration rate increases removal of organic matter and nitrogen and enhances ammonia transformation. It is therefore recommended to apply high aeration rates in Johkasou system.
Highlights
Small-scale onsite domestic wastewater treatment systems named Johkasou have been widely used in Japans rural areas and are still developing the performance
At anoxic and oxic zones, the mean of oxidation reduction potential (ORP) ranged from -110.0 to -250.5 mV before adjustment and from -24.1 to 93.4 mV after adjustment for Johkasou A (JO-A), and from 102 to 116 mV before adjustment and from -101.4 to 49.5 mV after adjustment for Johkasou B (JO-B)
These results implied that the ORP increased by increasing oxygen supply and dropped when the oxygen supply was shortened
Summary
Small-scale onsite domestic wastewater treatment systems named Johkasou have been widely used in Japans rural areas and are still developing the performance. Johkasou systems treat for both black and gray waters from household wastewater. The effluent of Johkasous is generally discharged into a local environmental receiving body, which the biochemical oxygen demand (BOD) and total nitrogen (TN) should be less than 20 m/L [1]. Johkasou system is considered to be an effective means for wastewater treatment in rural areas, which are designed, located and maintained satisfactorily. Johkasou system consists of an anaerobic stage as a primary treatment unit (a primary settling tank) and a secondary anaerobic (anoxic) stage that both are equipped filter bed. The aerobic (oxic) stage is a biological treatment unit typically like; activated sludge process, aerobic submerged biofilter, fluidized bed reactor, or biofilm filtration reactor. A disinfection chamber is installed at end of the process to inactivate microorganisms and fecal indicator bacteria in the effluent before disposing to the environment
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