ASSESSMENT OF TREATMENT EFFICIENCY BY NON-ENERGY CONSUMING AERATION SYSTEM FOR FAECAL SLUDGE MANAGEMENT IN AN EMERGENCY HUMAN SETTLEMENT IN BANGLADESH

Rohingya issue is the world’s fastest growing force displacement crisis. Around 8,99,349 Rohingya people have been driven to seek sanctuary in Bangladesh. In this high densely populated emergency settlement, management of faecal sludge is now-a-days becoming a great challenge with the limited resources and space. Wastewater treatment is an indispensable part of faecal sludge management. This study was carried out to identify the wastewater treatment efficiency of the up-flow filtration system with constructed wetland.

15 samples in total were collected from the treatment plant. Total five sample collection points that were raw wastewater, the outlet point of 1st, 2nd and 3rd filter chamber, the outlet point of constructed wetland of the treatment plant. Samples were collected from each point in three consecutive days. Nine parameters of each samples were analyzed in the laboratory. With the help of the literature review, those parameters were selected. For the characterization of FS as well as wastewater, parameters include inorganic, solids concentration, biological constitutes, nutrients and pathogens should be considered (Henze & Comeau, 2008; Niwagaba et al., 2014; Tchobanoglous et al., 2000). Total suspended and dissolved solid as solids concentration; Biochemical Oxygen Demand (BOD), Chemical Oxygen Demand (COD), Total Nitrogen (TN), Ammonia (NH3), Nitrate (NO3-), Total Kjeldahl Nitrogen (TKN), Total Phosphorus (TP) and Phosphate (PO43+) as nutrients are mentioned as important for the characterization of domestic wastewater (Negwamba & Dinka, 2019; Dawood et al. 2017; Hegazy and Gawad, 2016; Kulkarni et al. 2018). From the background study, BOD, COD, pH, EC, nitrate, ammonia, phosphate, TDS and TSS were measured in this study for the assessment of the performance of the treatment plants.

The treatment plant was found good at the removal of excess nutrients though NH3 concentration was not within the standard limit. However, the nutrient removal percentages were high in comparison with other parameters. BOD5 concentration of the final treated water were high that is almost twice than the DoE permissible limit. It is due to that no complete biological unit was present in the treatment process Though the BOD5/COD value of raw wastewater was good enough for treatment. A very partial anaerobic process might happen both in the filtration chamber and constructed wetland. Conventional biological process consumes energy and costs to maintain and operate which is not sustainable in the context of Rohingya emergency settlement. In this study, considering the crisis of energy, a non-energy consuming aeration system has been recommended to incorporate into the existing treatment process. This aeration system has been analyzed theoretically and found efficient to improve the water quality.

罗兴亚人问题是全球发展最快的被迫流离失所危机。约899349名罗兴亚人被迫逃往孟加拉国寻求庇护。在这片人口高度密集的应急安置点中，受限于有限的资源与空间，粪便污泥（faecal sludge）管理如今已成为一项重大挑战。污水处理是粪便污泥管理不可或缺的组成部分。本研究旨在探究带有人工湿地（constructed wetland）的上向流过滤系统（up-flow filtration system）的污水处理效能。

本次研究共从处理厂采集15份水样。采样点共计5处，分别为原废水、第1、2、3级过滤池出水口以及处理厂人工湿地出水口。连续3天从每个采样点采集水样，共计对每份样品的9项指标开展实验室分析。这些指标的选取参考了相关文献综述。为表征粪便污泥及废水特性，需考量无机物、固体浓度、生物组分、营养盐与病原体相关指标（Henze & Comeau, 2008; Niwagaba et al., 2014; Tchobanoglous et al., 2000）。针对生活污水的表征，常用指标包括：以总悬浮固体（total suspended solid, TSS）和溶解固体（dissolved solid, TDS）表征固体浓度；生化需氧量（Biochemical Oxygen Demand, BOD）、化学需氧量（Chemical Oxygen Demand, COD）、总氮（Total Nitrogen, TN）、氨氮（Ammonia, NH3）、硝酸盐（Nitrate, NO3-）、凯氏总氮（Total Kjeldahl Nitrogen, TKN）、总磷（Total Phosphorus, TP）及磷酸盐（Phosphate, PO43+）作为营养盐类指标（Negwamba & Dinka, 2019; Dawood et al. 2017; Hegazy and Gawad, 2016; Kulkarni et al. 2018）。基于前期背景研究，本研究测定了BOD、COD、pH、电导率（EC）、硝酸盐、氨氮、磷酸盐、TDS及TSS共9项指标，以评估处理厂的处理效能。

研究发现，该处理厂对过量营养盐的去除效果良好，但氨氮浓度未达标准限值。不过，相较于其他指标，其营养盐去除率较高。最终处理出水的五日生化需氧量（BOD5）浓度偏高，几乎达到美国能源部（DoE）允许限值的两倍。这是因为处理流程中未设置完整的生物处理单元——尽管原废水的BOD5/COD比值足以支持后续处理。过滤池与人工湿地中仅发生了极少量的厌氧反应。传统生物处理工艺需消耗能源并产生运维成本，在罗兴亚人应急安置点的场景下不具备可持续性。鉴于本次研究面临的能源危机，本研究建议在现有处理流程中加入无能耗曝气系统。经理论分析，该曝气系统可有效改善出水水质。