Petrochemical and food processing industries generate environmentally hazardous wastewaters that contain oil, volatile organic compounds (VOCs), and heavy metals. Such non-biodegradable contaminants require a complicated treatment process before disposal owing to their heterogeneous components. However, the conventional treatment process has relatively low removal efficiency and produces secondary pollutants. Here, we developed a hybrid treatment system with a high removal efficiency of suspended solids (SS), VOCs, and heavy metals during the pre-, main-, and post-treatment steps, respectively. In the pretreatment, dissolved air flotation with a modified slit nozzle, which generates size-tunable micro/nano-sized bubbles, removed 93.5% of the chemical oxygen demand (COD). The increase in the size of the bubbles in the range of 2–20 μm led to the effective removal of oil particles with a size comparable to that of the bubbles even with a low amount of coagulant. In the main treatment process, VOCs were degraded by an electrochemical advanced oxidation process (EAOP). Boron-doped diamond (BDD) electrodes were capable of degrading the non-degradable compounds 1, 4-dioxane, dichloromethane and tetrachloroethylene without generating sludge, compared to the low removal efficiency of the single and composite catalyst-doped dimensionally stable anodes. Due to the wide potential window, BDD was capable of generating hydroxyl radical. Such strong oxidant was the main factor in the high degradation efficiency. The environmentally friendly hybrid system was applied to the food and laundry wastewater treatment. In the pretreatment process, 99.7% of the oil was removed, and 95% of the COD was removed by the dual BDD–DSA electrodes in the EAOP. In the post-treatment process, more than 90% of heavy metals, including Cu, As, and Pb, were removed by a magnetic biochar adsorption process, and 90% of the biochar was recovered after the process.

石化和食品加工行业产生对环境有害的废水，其中含有油，挥发性有机化合物（VOC）和重金属。这种不可生物降解的污染物由于其异质成分而需要在处置之前进行复杂的处理。然而，常规处理工艺具有相对较低的去除效率并产生二次污染物。在这里，我们开发了一种混合处理系统，分别在预处理，主处理和后处理步骤中具有较高的悬浮固体（SS），VOC和重金属去除效率。在预处理过程中，使用改进的狭缝喷嘴气浮，产生大小可调的微米级/纳米级气泡，去除了93.5％的化学需氧量（COD）。气泡尺寸在2–20μm的范围内增加，导致即使有少量凝结剂，也能有效去除尺寸与气泡相当的油颗粒。在主要处理过程中，VOC通过电化学高级氧化过程（EAOP）降解。与单一和复合催化剂掺杂的尺寸稳定阳极的去除效率低相比，掺硼金刚石（BDD）电极能够降解不可降解的化合物1、4-二恶烷，二氯甲烷和四氯乙烯，而不会产生淤渣。由于潜在的窗口很宽，BDD能够产生羟基自由基。这种强氧化剂是高降解效率的主要因素。环保混合系统已应用于食品和洗衣废水的处理。在预处理过程中，通过EAOP中的双BDD-DSA电极去除了99.7％的油，并去除了95％的COD。在后处理过程中，通过磁性生物炭吸附工艺去除了90％以上的重金属，包括Cu，As和Pb，并且在该工艺后回收了90％的生物炭。