School of Water, Energy and Environment, Cranfield University, Bedfordshire, MK43 0AL, UK.
Department of Chemical Engineering, The University of Melbourne, 3010, Australia.
J Environ Manage. 2021 Dec 15;300:113730. doi: 10.1016/j.jenvman.2021.113730. Epub 2021 Sep 16.
In order to obviate the economic issues associated with pit latrine emptying and transport such as high water additions and rheologically difficult sludge properties, the implications of prompt solid/liquid separation were investigated. This was achieved through rheological characterisation of fresh human faeces and synthetic faeces, and comparison with aged faecal sludges. Shear yield stress, thixotropy and post-shear structural recovery were characterised for a total solids (TS) concentration range of 5-35% total solids (TS) and stickiness yield stress was determined for concentrations up to 100% TS. Fresh faeces rheology proved to be favourable when compared to aged matrices, evidenced by a lower shear yield stress and higher gel point solids concentration, suggesting that aging could alter the physico-chemical properties of faecal sludge. Fresh and synthetic faeces exhibited similar shear thinning, thixotropic behaviour with the majority of structural breakdown occurring at a low shear rate of 10 s, and the extent increasing with higher solids concentrations. At 32% TS, fresh faeces shear yield stress was permanently reduced by 80%, suggesting that low shear pumping could reduce the energy demand required for faeces transport. The sticky phase, which represents the region to avoid faecal transport and mechanical drying processes, was identified to range from 30 to 50% TS, with 25% TS as ideal to commence dewatering processes. This also coincides with the average solids concentration of faeces, which is achievable by source separation. This study has identified that handling of fresh faeces as opposed to aged faecal sludges would result in economic and environmental benefits, with energy, water and labour savings.
为了避免与坑式厕所清空和运输相关的经济问题，例如高加水量和流变学上困难的污泥特性，研究了快速固液分离的影响。这是通过新鲜人类粪便和合成粪便的流变特性以及与老化粪便污泥的比较来实现的。在总固体 (TS) 浓度范围为 5-35%总固体 (TS) 下，对剪切屈服应力、触变性和剪切后结构恢复进行了表征，并且在高达 100%TS 的浓度下确定了粘性屈服应力。与老化基质相比，新鲜粪便的流变学被证明是有利的，这表现在剪切屈服应力较低且凝胶点固体浓度较高，表明老化可能会改变粪便污泥的物理化学性质。新鲜和合成粪便表现出相似的剪切变稀、触变行为，大多数结构破坏发生在低剪切速率 10 s 处，并且随着固体浓度的增加而增加。在 32%TS 时，新鲜粪便的剪切屈服应力永久降低了 80%，这表明低剪切泵送可以降低粪便输送所需的能量需求。粘性相，代表避免粪便输送和机械干燥过程的区域，被确定为 30%至 50%TS，25%TS 是开始脱水过程的理想选择。这也与粪便的平均固体浓度相吻合，通过源头分离可以实现这一浓度。本研究表明，处理新鲜粪便而不是老化粪便污泥将带来经济和环境效益，节省能源、水和劳动力。
