No abstract

No abstract

The number of complaints regarding offensive odors from service industries, such as restaurants and garages, has recently increased. In this study, we aimed to develop an adsorbent for hydrogen sulfide gas derived from domestic wastewater and reveal the mechanisms of its removal. The adsorbent used for hydrogen sulfide gas removal was prepared by mixing coal fly ash and blast furnace cement with a mixing ratio of 87:13 by mass percentage. The optimum calcination temperature of the adsorbent was 700 °C to achieve a high removal performance for both dry and humid hydrogen sulfide gas. The X-ray absorption fine structure analysis revealed that hydrogen sulfide was removed on the adsorbent by oxidizing to sulfate. A pilot-scale experiment was conducted to evaluate the removal performance of hydrogen sulfide gas derived from domestic wastewater using the developed adsorbent. For a week, the average removal percentage of hydrogen sulfide gas derived from domestic wastewater remained at 99.1%. Therefore, the developed adsorbent for hydrogen sulfide gas is promising and cost-effective for promoting the recycling of coal fly ash.

In small-scale domestic wastewater treatment facilities (Johkasou), it is an important subject to reduce the excess sludge withdrawn from the system, because many of human excrement treatment plants have insufficient capacity for receiving the sludge. In this study, we focused on the performance of aerobic digestion for raw sludge (RS) stored in an inflow tank of Johkasou and a mixture of RS and garbage (GMS) under continuous aeration (CA) and intermittent aeration (IA) conditions. The volume of the reactor was 10 l and the treatment was conducted at 10 days of hydraulic retention time (HRT). The sludge obtained from the mixed liquor in the reactor was separated one to three-days interval by a centrifugal separator and returned to the reactor, and the supernatant was withdrawn as an effluent. After the operation, RS or GMS was fed into the reactors. The MLSS in the reactors increased gradually until around 150 days of the experimental period and kept stable concentrations after then (total experimental period: 229 days). The average sludge decomposition ratios for RS were 72.8％ under CA condition and 67.8％ under IA condition. The average sludge decomposition ratios for GMS were lower than those for RS: 64.7％ under CA condition and 53.3％ under IA condition. In the case of IA condition, both total nitrogen (TN) removals for RS and for GMS were ca. 95％. When RS was treated under CA condition, pH of the effluent decreased to 5.2, but almost complete nitrification was observed.

In the Johkasou system ῍an on῍site domestic wastewater treatment system῎, excess sludge is withdrawn and transported to a human excrement treatment facility. The operation of this system occupies a large part of the total treatment cost. Therefore, it is beneficial for reducing the production of excess in the system. The work presented in this paper focuses on the development of aerobic digesters for this purpose. Two types of reactors were set῍up : Reactor῍A was equipped with a filter unit for sludge separation and Reactor῍B was a kind of submerged bio῍filter process.The sludge obtained from an anaerobic tank in a Johkasou system was fed once a day into the reactors at HRTῐ ῏῎ days. Both reactors retained about ῏῎῎῎῎ mgῌL ῏῏ of MLSS. Effective solid separation performance was obtained, and the effluent contained about ῏ῒῑ of the fed SS. After approximately ῏῎῎ days of operation from start῍up, the SS reduction ratios ranged from ῐ῎ to ῑ῎ῑ. However, the SS reduction ratios in the first half of the period were lower due to the acclimation of biomass in the reactors. CODMn was effectively removed at ΐ ῍ ῑ and the CODMn level of the effluent was similar to, or lower than, that of raw domestic wastewater.