From lrbulluck@UCDAVIS.EDU Sat Jul 22 09:49:08 2000 Date: Fri, 21 Jul 2000 09:38:22 -0500 From: Russ Bulluck Reply-To: Sustainable Agriculture Network Discussion Group To: SANET-MG@LISTS.IFAS.UFL.EDU Subject: Re: Biosolids marc@aculink.net wrote: > sanet-mg-digest wrote: > > > > sanet-mg-digest Thursday, July 20 2000 Volume 01 : Number 1935 > > > > ---------------------------------------------------------------------- > > > > Date: Wed, 19 Jul 2000 18:36:19 -0400 > > From: "Gord Hawkes" > > Subject: Biosolids as fertilizer > > > > Greetings all from the wet and cool far north. Our large municipality is > > spreading biosolids from the regional sewage plant on farmland. There is a > > group that has been established to oppose the spreading of these biosolids. > > Although I am opposed based on my limited knowledge of the potential > > impacts, I am uncomfortable with the NIMBY mindset. I am a believer that > > if you do not bring solutions to the table then you are part of the > > problem. > > > > I am therefore asking for references to studies done on the use of > > biosolids as fertilizer and more importantly, how biosolids or sewage can > > be treated or processed to have little to no adverse affect on the > > environment. > > > > Best regards, > > > > Gord Hawkes > > Log Cabin Orchard > > Osgoode, ON > > Canada, eh! > > > > A recent news release from the sunny land of Florida has > indicated that the use of composting worms can cause a > conversion of questionable sewage sludge to a sludge with an > "A" rating. Significant improvement, eh? > Composting of biosolids also works well to destroy pathogens associated with municipal biosolids. (I've used composted biosolids in forest tree nurseries to control Cylindrocladium root rot, which a group of us are trying to put together for publication now). The problem with composted biosolids (or uncomposted, along with it's additional potential pathogen load) is that heavy metals are present, and applications of biosolids can lead to contamination of soil with heavy metals (such as lead, copper, selenium, thalium, barium, cadmium, and Zinc). There will be a lifetime loading rate for every biosolid, or biosolid compost. The biosolid compost I was using had a lifetime loading rate of 400 tons per acre, based on copper contamination. While that sounds like a lot, keep in mind that to achieve good N fertilization, 40 tons/acre needed to be applied. If this was done on a bi-yearly basis, (a common practice in forest tree nurseries, where second year seedlings are taken out for transplanting), then maximum loading of the soil would be reached in 20 years! Hardly a sustainable practice. However, by mixing the biosolid compost with spent mushroom compost (material on which mushrooms were grown for 18 months, then composted further for an additional 18 months), fertility and plant disease control could be attained using between 10 and 25 % of the biosolid compost, effectively extending the usefulness of the fields to 80 to 200 years (assuming maximum fertility requirements bi-yearly). The important thing to know is where the biosolids (or biosolid compost, which I'd recommend) came from, and what is the composition. Not only what is the N-P-K component, but what about the Cu-Pb-Cd-Th-Se-Zn-Ba component. If the biosolid is from an industrial area, the likelyhood of metals contamination is increased, but even a "bedroom community," where mainly residential buildings make up the municipal water treatment, can have high levels of some metals (most commonly copper and lead). Anyway. . . that's my two cents worth (looking back over the text I've typed, it's probably more like 2 bucks worth ;-) Russ -------------------- Russ Bulluck Visiting Post-Doctoral Scholar Department of Plant Pathology 1 Shields Ave UC-Davis Davis, CA 95616 lrbulluck@ucdavis.edu ------------------------------------------------------------- The soil population is so complex that it manifestly cannot be dealt with as a whole with any detail by any one person, and at the same time it plays so important a part in the soil economy that it must be studied. --Sir E. John Russell The Micro-organisms of the Soil, 1923 -------------------------------------------------------------