Compost heavy metals

Farm manures, sewage sludges, domestic composts—heavy metals, viruses, pathogens, organic pollutants... 

The suggestion frequentiy is made that substitution of organic fertilizers, namely manures and composts, for chemical fertilizers would be of ecological benefit. The reaUty is, however, that the supply and logistics of such materials could never be adequate for the present-day level of agriculture. Furthermore, iatensive appHcation of such materials to the soil would itself present ecological problems, such as mn-off pollution and steady buildup of toxic heavy metals. 

Evaluating the use of composts for reduction of the bioavailability and phytoavailability of lead and other heavy metals in contaminated soils... 

Simeoni L.A., Barbarick K.A., Sabey B.R. Effect of small-scale composting of sewage sludge on heavy metal availability to plants. J Environ Qual 1984 13 264-268. 

Normal agricultural practices generally cause an enrichment of heavy metals in soil, particularly Zn, Cu and Cd, due to the application of manure or its derivatives, compost or sludge and inorganic fertilisers and other human activities such as... 

However, if the raw materials are contaminated or the composting process is incomplete, unfavorable effects must be expected. Heavy metals may be introduced into the compost with communal waste. To ensure that these do not enter the food chain, authorised limit values must be strictly adhered to. The same is true of organic contaminants (particularly polyaromatic or chlorinated hydrocarbons), the effect of which is extremely complex. If the fermentation process is not satisfactory, putrefaction will occur, the by-products of which (S02, NH3, N02, organic acids, cadaveric alkaloids, etc.) inhibit plant growth and attract pests. 

Acid-digestion is often used with composts derived from municipal wastes, sewage and slurry, where toxic amounts of heavy metals may cause problems on the land to which they are applied. It is probably more convenient to determine total elements in soils by a benchtop X-ray fluorescence spectroscopy (XRF) instrument. This only requires the soil to be ground, and several reference standards of a similar soil. A Reference Materials Catalogue, Issue 5, 1999, is available from LGCs Office of Reference Materials, Queens Road, Teddington, Middlesex TW11 OLY, UK. Tel. -i-44 (0)20 8943 7565 Fax h-44 (0)20 8943 7554. 

The primary disadvantage to using tire chips for sludge composting was the initial cost of the chips. Generally, no equipment modification is required. Tire chips cost about 60 to 80 per ton whereas wood chips are around 15 to 20 per ton. Another disadvantage is that any effect of dilution of contaminants in the sludge (particularly heavy metals such as lead and cadmium) by wood chips is lost (41). Since rubber does not decompose, none of it stays with the compost as wood chips do. Another concern that has been expressed is that zinc from the tires may somehow adversely affect the compost. It is not clear at this time whether these are valid environmental concerns. 

Horn, A. L., During, R. A., and Gath, S. (2003). Comparison of decision support systems for an optimised application of compost and sewage sludge on agricultural land based on heavy metal accumulation in soil. Sci. Total Environ. 311(1—3), 35—48. 

Hani, H. 1991. Heavy metals in sewage sludge and town waste compost. In E. Merian, Ed. Metals and Their Compounds in the Environment Occurrence, Analysis, and Biological Relevance. VCH Publishers, New York, pp. 357-368. 

Laboratory tests have to be performed for materials, intermediates and additives. In these tests the chemical properties are checked, the ultimate biodegradability is verified and the disintegration properties are determined. Chemical testing serves to ensure that neither harmful organic substances, such as polychlorinated biphenyl (PCB) and dioxins, nor heavy metals, such as lead, mercury and cadmium, pass into the soil via the compost. 

Barker, A.V. and Bryson, G.M. 2002. Bioremediation of heavy metals and organic toxicants hy composting. The Scientific World Journal, 2 407-20. 

Chaney, R.L., Ryan, J.A., Kukier, U., Brown, S.L., Siebielec, G., Malik, M., and Angle, J.S. 2001. Heavy metal aspects of compost use. In Compost Utilization in Horticultural Cropping Systems. Stoffella, P.J. and Kahn, B.A. (Eds). Lewis Publishers, Boca Raton, FL, pp. 323-59. 

Pinamonti, F., Nicolini, G., Dalpiaz, A., Stringari, G. and Zorzi, G. (1999) Compost use in viticulture Effect on heavy metal levels in soil and plants. Commun. Soil Sci. Plant Anal, 30, 1531-1549. 

Engineered reed-bed and constructed wetland systems for removal of heavy metals from wastewater using phytoremediation are in use in some developed Asian countries. The root system of the hyper-accumulator plant penetrates a permeable rock bed. The wastewater is introduced into one end of the bed and flows through the permeable rock layer. The rock layer should be inert to heavy metals binding so that it does not unwittingly serve as a sink for heavy metals. These metals are sequestered by the root system and translocated to the shoots. Periodically, the metal-containing shoots are harvested. The biomass can be burned off or composted to yield a low volume of metal-rich ash. 

Qty compost and sewage slurries may be contaminated by the toxic organic compounds and heavy metals. 

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