Evaluation of a Novel Sewage Treatment System by Combining a Primary Settled Basin with DHS Reactor

Abstract

At present, 95 % of the total population of the Egypt country takes up residency in areas around of Nile, irrigation agriculture caused by using raw sewage exacerbate the issue of environmental health hazard risk in arid regions of Egypt. So, Egypt country goes ahead with effective utilization of treated sewage for irrigation, our international research consortium has proposed a novel concept of sewage treatment technology for risk reduction of health hazard and we focus on down-flow hanging sponge reactor (DHS) as sewage treatment technology. DHS behaved extremely well as sewage treatment technology in India and it is widely expected to dominate in a developing country. The method is a combination of the DHS for posttreatment and primary sedimentation tank for pretreatment. This method went live in Egypt in 2014. So, KNCT tried demonstrating experiment in Japan with the use of share of the same design as method. Preliminary experiment has confirmed the feasibility to satisfy a criterion for irrigation in EGYPT as an objective. Irrigation standard (TSS < 60 mg/L, BOD < 60 mg/L, COD_total < 80 mg/L, ${\text{NO}}_{3}^{ - }$ < 50 mg/L) set by Egypt government has achieved effective utilization of treated sewage for irrigation as objective. When hydraulic retention time (HRT) set 1 h as DHS’s volume load of target, condition of operation of experiment is controlled by varying treatment quantity of sewage. We started up the experiment provided that treatment quantity of sewage: 5 m³/day, HRT: 4 h. The experiment is performed in five stages. It has continued since March 2013 (Phase 1: HRT 4 h, Phase 2: HRT 2 h, Phase 3: HRT 1 h, Phase 4: HRT 2 h, and Phase 5: HRT 4 h). The preliminary experiment indicates the possibility of effective utilization of treated sewage for irrigation. The removal rate of biochemical oxygen demand (BOD) and suspended solids (SS) retains sufficient strength to meet irrigation standards. (Phase 1: 82 %(BOD) 97 %(SS), Phase 2: 92 %(BOD) 81 %(SS), Phase 3: 76 %(BOD) 65 %(SS) Phase 4: 81 %(BOD) 68 %(SS), Phase 5: 89 %(BOD) 88 %(SS)). The result of the profile analysis indicated that organics destruction occurred from the top of the reactor (1st stage) to the 3rd stage and the nitrification process proceed from the 4th stage to the 5th stage. On the other hand, the nitrification process of ${\text{NH}}_{3}^{ - }$–N was poor at Phase 3. We believe that this related to a blocked gap of media sponge. At Phase 4 and Phase 5, the removal rate of BOD and nitrification of the water was provided so as to lengthen the processing time. Improvement in the ability to remove ${\text{NH}}_{3}^{ - }$–N is vital to use the primary settled-DHS process for irrigation, because ${\text{NH}}_{3}^{ - }$–N is a toxic substance for agricultural irrigation.