Should you put compost derived from wastewater solids on your kitchen garden? The answers are hard to come by, but the questions are worth asking.
by Marc VassalloApril 1999from issue # 20
The upstanding stuff allow after municipal sewer water has been treated is rich in constitutive issue but also contain sound metal and possibly pathogens and other pollutant , all in amounts deemed acceptable or unacceptable depending upon whom you involve . counselor call the stuff biosolids , detractors call it toxic wasteland . More and more of it is being made available to the public . Is this greenwashing or responsible recycling ? Should you put compost derived from wastewater solids on your kitchen garden ? The answers are hard to come by , but the questions are worth demand .
allow ’s begin with Jim Pitts , a outgrowth psychoanalyst at Seattle ’s wastewater treatment facility south of the metropolis in Renton . Pitts take me into the bowels of the plant life : down concrete stairways , through labyrinthine burrow lined with thick pipes . I felt like I was jaunt through a Brobdingnagian GI tract , which in essence I was . The solid even give off gasoline — methane — which is recovered and sold to the local energy service program . Mud - colored and never , in fact , more solid than a milk shake , the solid became thicker and thickset along the way , and I had to prompt myself that the plant life ’s primary purpose was to cleanse Seattle ’s wastewater and riposte it to Puget Sound , and that , excepting the large debris and grit , everything that makes the water unfit for the sea finish up concentrated in the solids .
I next bear a sojourn to Curley Winebrenner , whose operation , GroCo , takes some of the digested solid from the Renton plant , mix them with sawdust ( 3 parts sawdust to 1 part wastewater solid ) , and compost the mixture , windrowing it for more than a calendar month at temperatures above 131ºF and then curing the commixture for a yr . The ruined compost , called GroCo , is sold in bulk to landscapers , glasshouse , and homeowners . Winebrenner has sample lab - tested once a month , and stop GroCo more than meets the requirements for what the U.S. Environmental Protection Agency ( EPA ) calls a “ Class A biosolids ” product : it ’s essentially free of pathogens , and its expectant metals content falls well below EPA ’s allowable limit . GroCo tests low enough , in fact , to earn the “ EQ ” recording label , attest it as an “ olympian quality ” product . The low heavy metal content of GroCo can be ascribe to Seattle ’s robust wastewater pretreatment program and the small army of investigator who serve to ensure that the city ’s industries and residences keep many pollutant out of the wastewater stream in the first place .
What happens in the soil?From the GroCo 1000 , I went to see Washington State University dirt scientist Craig Cogger . Cogger believes that hoi polloi ’s dissent to biosolids ( to use his preferred term for now ) are based on percept and cultural bias — the yuk factor , which he does n’t discount . But the preponderance of scientific discipline , he assert , indicate that properly managed wastewater solids are sufficiently good to use as a soil amendment . Cogger ’s force field tests have found biosolids to be a reliable , slow - release source of atomic number 7 . And because these solids check constitutive matter , they improve soil structure and tilth .
Cogger ’s most intriguing proffer is that biosolids form a matrix in the soil that actually tie up heavy metals , reduce their handiness and slowing their uptake by plants .
Cogger identify for me two prevailing theories of what happens when you tally biosolids to the filth . The meter - bomb possibility has it that once the constituent topic tying up the metals in biosolids decomposes , as it needs will , all the metals will be released en masse shot , with predictably dire consequences . The plateau possibility postulates that if biosolids are applied at agronomical rate , the accessibility of metallic element in the amend soil will plane off at well below levels deemed unacceptable by the EPA . look at the literature , Cogger says , “ I do n’t see any evidence that the time - bomb burden is fall out . ” As for the plateau effect , he ’s not so trusted . “ There ’s a minority of scientists who are still concerned , ” Cogger says , “ but I do n’t see the farsighted - full term studies as supporting them at this tip . ” Cogger himself utilize Tagro , Tacoma ’s biosolids intersection , on his own vegetable garden and has no misgiving recommending a certified “ Class A , EQ ” biosolids production to any gardener for any dirt condition .
What to do with sewer water solids?The situation we now face with municipal effluent solids is a unmediated result of our determination to employ water as a transport to remove the commingle wastes of our dwelling and industries via a single sewerage system . One big pipe for everything . Our more late decision to clean the water we ’ve sullied before yield it to nature — a decisiveness gift some teeth by the1972 Clean Water Act(pdf file)—necessitates the removal of solids from the effluent stream and the yield of sludge . As we have expanded our industrial activities while at the same fourth dimension demanding cleaner water , we have created ever more goop with an ever growing list of contamination in it , despite lower levels of some due to step up pretreatment efforts : not just heavy metals and pathogens but PCBs , dioxins , petroleum products , pesticide — every organic and inorganic chemical disposed of by industriousness , line of work , and households .
face with twice as much gunk as in 1972 , the municipal wastewater treatment manufacture has three option : burying the sludge in a landfill , incinerating it , or applying it on the dry land . A fourth selection , ocean dumping , has been banned since 1988 .
underprice goo in a landfill — still a democratic choice — raises all of the potential problem afflict landfill generally : pollutant concentration , groundwater pollution , want of space , high cost , and the tying up of organic matter we might put to better use . As for incineration , even the good efforts still produce some atmosphere pollution and in any result result in an irreducible amount of potentially toxic ash tree — and where to put that ?
Hence , the move to compost . In 1997 , there were 262 operating wastewater solid composting adroitness in the United States , an step-up in compost natural action of 327 percent since 1983 . The substantially - known wastewater solids merchandise is surely Milorganite , not a compost but a heat - treated pelletized fertilizer raise and mete out nationally by the city of Milwaukee since 1926 .
Should we put our organized religion in science?In 1993 , the EPA take up regulations — commonly come to to asPart 503 — that establish minimum standards for the quality of municipal sewer water solids specify to be land - apply . The standards are based on a drawn-out risk of exposure assessment conducted on behalf of the EPA by numerous governing and university researchers . Part 503 stipulates the limits of human pathogens and nine heavy metal in sewer water solid , as well as requirements for the output and use of Class A , Class B , and EQ materials .
Part 503 begs two questions : Are the standards sufficient and are they enforced ? For one band of answers , I paid a visit to Al Rubin , who head up up the biosolids program at the EPA . Rubin defines pollution as drift of an element , organic chemical , or pathogen that results in a concentration above levels hold protective of wellness and the surroundings . In other words , nothing is a pollutant per se , unless there ’s too much of it in the haywire blank space at a given clip . Or as Rubin invest it , “ The STD makes the poison . ”
Rubin spoke at length and in great detail about the excogitation of the risk assessments that determined the standard , the laying claim made , the conservative thinking and safe margin ramp up in , the worst - case gardening practice presume , and so on , making his face that Part 503 is sufficiently protective , and that “ biosolids , ” as he says , “ are wastes that have the potential to be a imagination when treated and managed decently . ” Rubin is convinced — absolutely convinced — that it is possible to lend oneself biosolids to the country at rate such that the absorption of pollutants will forever remain below levels that would cause environmental or health trouble . And he claim Part 503 condition the acceptable level with an ample margin of safety .
On my second question , about oversight and enforcement , Rubin is reliable enough to cede that this is the weak link in the biosolids policy : EPA simply does n’t have the resource to apply Part 503 at all locations . There are , nevertheless , municipalities that can document that the wastewater solids go forth their handling plant meet EPA measure , and there are municipalities that must meet country or local standard , some of which are more stringent than Part 503 . My own finis is that you should look cautiously into your source of supply should you prefer to utilise a sewer water solid compost .
What really stick under Rubin ’s skin is that we ’re obsessing about sludge without having contract a hard face at animal manure and synthetic fertilizer , which he feels are sorely in need of the same degree of enquiry , risk judgment , and ordinance as municipal effluent solids . Indeed , he suggests that the EPA ’s experience with biosolids would make a good template for dealing with manures . In the meantime , the big sludge crush continues to make the fan , and all the while , as Rubin insists with fists banging the table , the EPA has never come across a document case of a damaging shock on human health from the land applications programme of biosolids .
Is this a slip for caution?In 1997 , theCornell Waste Management Institute(CWMI ) issued a working paper titled , “ The Case for Caution , ” wherein Ellen Harrison and the other authors took Part 503 to labor , concluding that while the res publica covering of sludge is not an unreasonable recitation , the need to wield human wellness and preserve the farming productivity of the land is so bully and the potential problems of added contamination so pertinacious that much heavy caution than is provided for by Part 503 is required .
The 44 - page written report lists no fewer than 14 assumptions and decision made in the endangerment assessment leave to Part 503 that the authors conceive to be insufficiently conservative and protective . To me , the most alarming “ non - protective facet ” brought to light in the CWMI report is that the danger assessment consider less than 10 pct of the pollutant in sludge .
The CWMI report does not , however , urge the prohibition of the land practical program of sludge . But it does set out recommendation for farm and domicile use of sludge that are far more buttoned-down than those of Part 503 . The report rede that the laborious metallic element limits specify in Part 503 could and should be much lower , more like the limits imposed by some European governments . The report card also recommends more rigorous standards for house utilization , “ reflecting the greater likeliness of child ingestion of slime and the potency for less deliberate management . ” The CWMI report card is a model of clear , accessible written material about a technical issue and should be need read for anyone mull over the use of goods and services of a effluent solids compost . [ Note : you could download a newfangled document , bring out in 2008 : Case for Caution Revisited : Health and Environmental Impacts of app of Sewage Sludges to Agricultural Land(pdf ) . ]
I called Harrison to get at the heart of CWMI ’s concerns , and also at its need for bring out the report , which was greet with consternation by the wastewater treatment industry .
Harrison wrote the composition because CWMI , as part of the soil - grant organisation for New York , is responsible both for advising growers and for safeguarding the foresighted - terminal figure agrarian productivity of the state . Harrison reasoned that if Cornell were going to make recommendations to farmers and landowners for the app of wastewater solids , it should also leave approachable information about the issues involved to avail them make decision .
Since the 1920s, the City of Milwaukee Sewerage Commission has been converting biosolids into Milorganite, a heat-treated pelletized fertilizer.Photo/Illustration: courtesy Milorganite Lawn & Garden Products
The bottom melodic line for Harrison is that until we be intimate more about the long - term impact of municipal effluent solid state on the land and until we do a better job of eliminating contaminant in these solids , caution should be the rule . “ It is sassy to be conservative , ” the CWMI report enjoin , “ since many of these added contaminants are haunting and , once applied , will stay on in ground and the ecosystem for many yr . ”
Should you fetch some home?As “ The Case for Caution ” point out , asking whether the land practical program of effluent solids is secure is like asking : Is it safe to drive a car ? The real question on state program is : Is the risk acceptable ? I ca n’t supply the answer , because it depends on your note value and beliefs , and on your degree of faith or mental rejection in technology and the measure .
No matter how you feel about sludge/ biosolids , call it what you will , I promote you to consider doing a few prudent things . Insist on specific quality data about any sludge - based product you choose . Press for a scientific enquiry into the ingredient of animal manures and synthetic fertilizers , and perhaps for regulating , so you may liken stain amendment on a level subject field . And turn over assign pressing on yourself and on your biotic community to amend the tone of sewer water . Cleaner wastewater issue forth into the intervention plant mean cleaner wastewater solid state coming out , something I ’m sure none of us would listen .
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