Pollution Research Group, University of KwaZulu-Natal, Howard College, 4001, Durban, South Africa.
Chemical Engineering, University of KwaZulu-Natal, Howard College, 4001, Durban, South Africa.
J Environ Manage. 2018 Dec 15;228:149-157. doi: 10.1016/j.jenvman.2018.08.098. Epub 2018 Sep 12.
This work aims at characterizing the rheological properties of faecal sludge from Ventilated Improved Pit (VIP) latrines and their implication on pit emptying. Faecal sludge was sampled from 3 pit latrines located in the eThekwini Municipality (Durban, South Africa). Samples were taken at different positions within the pit. For each of the samples, measurements in the rheometer in triplicates were performed in order to determine their rheological properties, and their moisture and ash content were measured also in triplicates. Experiments in the rheometer were performed for samples for which its moisture content was modified. In order to better understand the influence of water addition into the pit. During pit emptying, calculations were carried out from the experimental data, based in the criteria set in the Omni-Ingestor initiative, carried out by the Bill & Melinda Gates Foundation. Faecal sludge exhibited a shear thinning behaviour, i.e. a decrease in viscosity with increasing shear rate, and presented a yield stress comprised between 500 to 1000 Pa. This needs to be surpassed in order to overcome the elastic resistance of the sludge to flow. Similar viscosities were found for the samples from the different pits, irrespective of the position within the pit, except for the sample from the bottom of one of the pits for which it was not possible to induce a flow. This sample had a considerably lower moisture content (67% wet basis) compared to the other samples (around 80% wet basis), probably due to a higher biodegradation as it was the most aged sludge in the pit. According to the experimental results and calculations, the pumping requirements during pit emptying will decrease drastically by increasing the moisture content of the sludge. The addition of water into the pit would then facilitate the pit emptying operation by reducing the head and power required for pumping. However, this practice would require employing considerable amounts of water and handling higher volumes of sludge, which would lead to longer pit emptying times and increase the difficulty of the operation. For example, increasing the moisture content of the sludge from 75 to 90% will reduce the head and power of the pump by a factor 100, but will triplicate the amount of water in the sludge and, consequently, the time for pit emptying. Therefore, a compromise has to be made between increasing the pumping feasibility and adding water to the pit.
本研究旨在对通风改良坑（VIP）厕所中的粪便淤泥的流变性及其对坑排空的影响进行描述。粪便淤泥从 eThekwini 市（南非德班）的 3 个坑式厕所中采集。在坑内不同位置采集样品。对每个样品进行 3 次重复测量，以确定其流变特性，并对其水分和灰分含量进行 3 次重复测量。在对水分含量进行了修改的样品上进行了流变仪实验。为了更好地了解向坑内加水的影响。在坑排空过程中，根据比尔及梅林达·盖茨基金会开展的 Omni-Ingestor 倡议的标准，从实验数据中进行了计算。粪便淤泥表现出剪切稀化行为，即随着剪切率的增加而降低的粘度，并且呈现出介于 500 到 1000Pa 之间的屈服应力。为了克服淤泥的弹性阻力，需要超过这个屈服应力。来自不同坑内的样品表现出相似的粘度，而不管坑内的位置如何，除了一个坑底部的样品外，对于该样品，无法诱导其流动。与其他样品（约 80%湿基）相比，该样品的水分含量（湿基 67%）低得多，这可能是由于更高的生物降解作用，因为它是坑内最陈旧的淤泥。根据实验结果和计算，通过增加淤泥的水分含量，坑排空期间的泵送要求将大大降低。向坑内加水会通过降低泵送所需的水头和功率来促进坑排空操作。然而，这种做法需要使用大量的水和处理更多体积的淤泥，这将导致坑排空时间延长，并增加操作难度。例如，将淤泥的水分含量从 75%增加到 90%，将使泵的水头和功率降低 100 倍，但会使淤泥中的水量增加两倍，从而使坑排空时间增加。因此，必须在增加泵送可行性和向坑内加水之间做出妥协。
