《深入打好城市黑臭水体治理攻坚战实施方案》的发布，让不少目光聚焦到了更为细致的地方，如：“建立健全垃圾收集(打捞)转运体系”，“不应盲目提高污水处理厂出水标准、新扩建污水处理... 《深入打好城市黑臭水体治理攻坚战实施方案》的发布，让不少目光聚焦到了更为细致的地方，如：“建立健全垃圾收集(打捞)转运体系”，“不应盲目提高污水处理厂出水标准、新扩建污水处理厂”，“到 2025 年，进水BOD 浓度高于 100 毫克/升的城市生活污水处理厂规模占比达90%以上”，“严格做好‘农家乐’、种植采摘园等范围内的生活及农产品产生污水及垃圾治理”，“黑臭water整治not力问题纳入中央生态环境保护督察和长江经济带、黄河流域生态环境警示片现场调查拍摄范畴”，“落实pollution water treatment收费政策”,”推广以pollution water treatment factory进water pollution物浓度、pollution material削减量和pollution mud handling处置量等支付operating service fee”等等。本文就这个问题来探讨一下。
BOD是什么？
BOD，biochemical oxygen demand，即在一定条件下微生物分解存在于water中的可生物降解有机物所进行的生物化学反应过程中所消耗的溶解氧数量，是反映water中有机污染物含量的一个综合指标，也是重要的water quality pollution参数。一般清净河流的五日生物化需氧量不超过2mg/L，工业、农业、fishery用water等要求生物化需氧量应小于5mg/L，而life drinking water应小于1mg/L。城镇排放标准中明确，BOD5的一次监测最高允许排放浓度为一级A15mg/L；一级B30mg/L二级45mg/L三70mg/L。
为什么进water BOD低了也不行？
从上述定义看，BOD数值高就表明有机污染物含量高，但按out-water standard看，不难发现，这并不意味着进water BOD数值越低越好，其矛盾症结点还是在于clear-water and polluted-water是否分流。
从BOD看雨-polluted分流和pipe network improvement
专家普遍认为，进water BOD浓度过低的大部分可以归结到non-life-polluted wastewater排入稀释，以及pipe network flow speed too low（大量BDO沉积在pipe network内）的因素上，因此才会有this kind of attention to "progressive input of biological oxygen demand". It is the actual concern about the mixing of sewage and rain in urban drainage systems, as well as the lack of scientific planning or aging issues in pipe networks.
Rain-polluted separation reconstruction, everyone knows, which refers to the process of pipe network construction. Pipe networks have been repeatedly mentioned and are a major issue that has been brought up many times in urban flood control and drainage construction. Currently, there are certain blind spots in China's urban pipe network construction, with old-age issues, delays in reconstruction and repair adding complexity to the situation.
Moreover, there is also a phenomenon called "heavy factories and light pipes", where pipe networks receive less attention than they deserve. The idea of upgrading pipe networks must keep pace with progress; another issue is related to pricing mechanisms - supporting infrastructure for expanding or improving pipes is indeed a heavy burden.
According to preliminary estimates by industry insiders, new pipeline construction costs approximately RMB 170 million per kilometer on average; if we aim at eliminating all open discharge outlets for domestic waste waters within built-up areas by the end of this period (the so-called "14th Five-Year Plan"), then investment into wastewater pipelines + rain runoff pipelines would exceed RMB 2 trillion during this period.
It's worth noting that Phase II system-wide full-scale promotion work for sponge city development demonstration projects has already kicked off since last year; application guidelines explicitly state that by project completion date (i.e., end-2024), all cities' sewage plants should reach an average progressive input concentration above 100 mg/liter.
Based on this policy direction alone, it can be anticipated that enthusiasm for upgrading local municipal infrastructure will escalate further among relevant enterprises who could benefit from these opportunities.
Thus while discussing “how much does it cost per ton?” one must first recognize how closely linked these seemingly unrelated concepts actually are: our pursuit after improved environmental health requires not just enhanced plant efficiency but also strategic investments towards bettering our very foundation – urban drainage systems themselves – which underpin all efforts towards cleaner air & water through effective management strategies such as clear-cutting mixed industrial-commercial residential zones & promoting green technologies like solar-powered pumps!
