这家公司将城市污水变废为宝

刘颖

The water authority in Washington, D.C., receives 1,500 wet tons of sewage into its wastewater-treatment facility each day. CEO George Hawkins views it as liquid gold—an ingredient for a moneymaking operation that could help pay for repairs to its aging infrastructure. His agency, DC Water, cooks, sterilizes, and turns that sewage into a soil fertilizer called Bloom, which began shipping this spring to nurseries and garden centers in the region.

Ignore the “ick” ¬factor. DC Water is among a handful of utilities that is innovating to save or generate money. Philadelphia’s utility is using the water that washes into the sewers during storms to keep its parks green. And in Portland, Ore., purified wastewater is being used to make beer. (No one says you have to drink it.)

The Washington initiative is ambitious. The process begins with the matter flushed down a toilet, which may travel through any of DC Water’s 1,800 miles of sewer pipes to the wastewater-treatment plant. Oils, fats, sediments, and objects are screened out, and the water is disinfected. The remaining sludge then goes through a three-stage process that cooks it in high heat and pressure, sterilizing and softening it. The clean sludge is then sent to four 80-foot-tall anaerobic digesters, where giant mixers churn the liquid for two weeks while a population of microorganisms called “methanogens” eats the organic matter, producing methane gas for electricity that ultimately powers a third of the water plant’s operations. The solids then travel to a belt-filter press that squeezes out water and delivers the crumbly compost to bunkers that can hold 1,000 tons each.

The result can be used to fertilize gardens and trees. (Bloom fertilizer is in high demand, says Brian Riddle, who bought 1,000 tons of it for his D.C.-area garden centers, Homestead Gardens. He says it’s hard to find affordable fertilizer that’s safe and natural. “Bloom,” he says, “is loaded with valuable nutrients.”)

DC Water spent several years investigating and testing the technology, which was already in use in Europe, before spending $470 million on the equipment two years ago. DC Water would have needed to spend most of that money anyway to treat the biosolids, and this was a way to do that in a sustainable manner and generate revenue to fix aging pipes. More than half of the D.C. pipes are 79 years or older—some date to 1860—and the agency estimates a need for at least $1 billion in repairs in the coming years.

Bloom’s sales are still fledgling, and Hawkins says it may take two or three years to ramp up. But the approach was a necessity. “It’s literally like a startup,” he says. “Our business model was going to fail without fundamental change.”

That could be the case for much of America’s broad array of infrastructure, says Greg DiLoreto, past president of the American Society of Civil Engineers, which produces a report card on the state of the nation’s infrastructure every four years. America’s grade this year: D+. The nation’s 14,748 water-treatment facilities are in particular disrepair, suffering from 240,000 pipe breaks a year. Those facilities will need to serve some 56 million new customers over the next two decades, says DiLoreto.

He praises DC Water’s initiative. “That kind of innovation will make the money go a lot further,” says DiLoreto, “but we still need investment or we’re going to see more pipe breaks and more Flint, Michigans.”

DC Water’s new investment has allowed it to cut its operating budget, as well as its biosolid disposal and energy costs, making it the largest generator of clean energy in the Washington, D.C., area. The utility has even more plans to generate revenue, including selling “sewer-thermal energy,” which uses heat exchangers inside the city’s underground sewage system to heat and cool buildings—much like traditional geothermal energy drawn from the earth’s core. The sewer energy is being tested at several of DC Water’s own buildings before being rolled out to potential customers. Other plans are in the works too. They give new meaning to the old phrase “Waste not, want not.” 

刘颖

美国的华盛顿特区水务部门的废水处理设施每天都要处理1500吨废水。该部门的CEO乔治•霍金斯将这些废水看作“液体黄金”。这是一项相当赚钱的业务，赚来的利润可以帮助该部门修理其老化的基础设施。他领导的DC Water部门主要负责对废水进行处理、消毒，然后将其转化成一种名叫Bloom的土壤肥料。从今年春天起，这种肥料已经开始向该地区的苗圃和花卉商店供应。

一想到下水道的废水，很多人都会有作呕的冲动。但通过创新废水处理方式来省钱或赚取利润的机构远不止DC Water这一家。比如费城的公用事业部门就将暴雨时冲进下水道的水储存起来，用于公园的绿化灌溉。而在俄勒冈州的波特兰市，净化的废水已经被用来酿造啤酒了。（当然，没人强迫你非得喝这种啤酒。）

华盛顿水务部门的废水处理计划可谓雄心勃勃，整个过程首先从冲马桶开始。DC Water在全城拥有1800英里长的下水道，你家马桶的水会经由其中的一根管道汇入该部门的污水处理厂。其中的油脂、脂肪、沉积物和杂质会被过滤掉，过滤后的水会被消毒，而过滤出的污泥则要经过高温高压、消毒、软化等三个步骤的处理，随后这些干净的淤泥会被送入一个厌氧的沼气池中。在那里，它们会被巨大的搅拌机搅拌两周的时间，使一种叫做“产甲烷菌”的微生物分解掉淤泥中的有机物，从而产生用于发电的沼气。这些沼气发出的电力可满足该污水处理厂三分之一的生产用电。剩下的淤泥会被带式压滤机再次挤压，排出其中的水分。然后它们会被填进堆放肥料的大坑中储藏，每个大坑可储藏1000吨这样的污水加工肥料。

这些肥料可以用于给花园和树木施肥。（据在华盛顿地区经营Homestead Gardens花卉商店的布莱恩•里德尔称，市场对Bloom牌的肥料有着很高的需求。他表示，市面上很难找到像Bloom肥料这样既物美价廉、又安全天然的肥料。他说：“Bloom肥料富含各种有价值的营养物质。”）

DC Water已经花费了好几年时间对这项技术进行研究和测试。之前这项技术已经在欧洲得到了应用。两年前，DC Water斥资4.7亿美元订购了相关设备。何况就算不购买这些设备，DC Water迟早也得把这笔钱尽数花在废水处理上。而这种处理方法不仅具有可持续性，还可以产生不少的收益，这笔钱则可以用来维修老旧的污水管道。DC Water的下水道大半都使用了79年以上，有些甚至是1860年修建的。据该部门预计，未来几年，他们至少要花费10亿美元用来维修这些管道。

目前，Bloom肥料的销售仍然处于起步阶段，霍金斯表示，Bloom品牌可能还需要两三年才能初具规模。但这种模式显然是必要的。“我们就像一家创业公司一样，如果我们不进行根本性的改革，我们的业务模式就必然会失败。”

美国土木工程师协会的前任主席格雷格•迪雷奥托指出，美国大部分的基础设施可能都面临着类似DC Water的境地。美国土木工程师协会每四年会发布一份关于美国基建设施现状的报告。今年的报告给美国的基础设施打出了D+的分数。美国各地有14748个水处理设施尤其亟须维修，全美每年破裂的污水管道达到了24万根。而且迪雷奥托指出，未来20年，这些设施还得额外为5600万名新用户服务。

迪雷奥托也表扬了DC Water的创新：“这种创新会使资金发挥更大的效用。但我们仍需要进一步的投资，否则我们就会看到更多的污水管道破裂，遭遇更多的密歇根州弗林特市发生过的那种饮水危机。”

归功于这笔新投资，目前DC Water的运营预算已经有所削减，它的生物废料和能源成本也同样有所下降，同时它也成了华盛顿地区最大的清洁能源发电企业。该部门还制定了更多的计划来增加收入，比如销售“废水热能”——该技术可以利下水道系统安装的热交换器来对建筑物提供冷气或采暖，原理很像传统的地热能。在向潜在客户推广之前，DC Water已经开始在自己的几栋办公楼里进行试验了。他们的这些创新做法也给“俭以防匮”这句老话赋予了新的意义。