The presence of suspended solids (SS) in raw feed-water can reduce the efficacy of Ultraviolet (UV) irradiation (Chem. Eng. Sci. 143 (2016) 55–62). Therefore, an integrated SS pre-treatment with rapid sand-filters (SF) is sometimes used. Here we synthesize for the first time a Fr 13 risk assessment of a two-step integrated SF with a UV reactor (SF-UV). The aim was to simulate how stochastic fluctuations in steady-state plant parameters could impact UV efficacy for potable water production. Failure of the SF-UV is defined as unwanted survival of viable Escherichia coli. Results show the overall failure of SF-UV operations is 40.4% which equates to 148 failures per annum. The mean reduction in SS in the SF was log₁₀ −1.11 (90%), with a subsequent reduction in viable E. coli in the UV reactor of log₁₀ −2.93 (99.9%). SF-UV is shown to be a combination of successful and failed operations and not all failed SF automatically result in failure in overall SF-UV efficacy. The second-tier simulation showed that the greater the safety tolerance the greater the loss of flexibility in SF-UV reactor. A precision feed-water flow control is needed to minimize underlying vulnerability to unexpected failure. This work will be of immediate interest to risk analysts, benefiting operators and managers responsible for producing potable water using UV irradiation.

原料水中悬浮固体 (SS) 的存在会降低紫外线 (UV) 照射的功效 (Chem. Eng. Sci. 143 (2016) 55–62)。因此，有时会使用带有快速砂滤器 (SF) 的集成 SS 预处理。在这里，我们首次合成了带有紫外线反应器 (SF-UV) 的两步集成 SF的Fr 13风险评估。目的是模拟稳态工厂参数的随机波动如何影响紫外线对饮用水生产的功效。SF-UV 的失败被定义为活大肠杆菌的不必要的存活。结果表明，SF-UV操作的总体故障率为40.4％，相当于每年148次故障。SF 中 SS 的平均减少为 log ₁₀-1.11 (90%)，随后紫外线反应器中活大肠杆菌的减少为 log ₁₀ -2.93 (99.9%)。SF-UV 被证明是成功和失败操作的组合，并不是所有失败的 SF 都会自动导致整体 SF-UV 功效的失败。二级模拟表明，SF-UV反应器的安全容差越大，灵活性损失越大。需要精确的给水流量控制，以最大限度地减少对意外故障的潜在脆弱性。这项工作将引起风险分析师的直接兴趣，使负责使用紫外线照射生产饮用水的操作员和管理人员受益。