Feedstocks

Introduction

All Feedstocks which can be digested successfully in an anaerobic digestion plant must be organic, typically proteins, fats and carbohydrates.   Synthetic organics are mainly derived from petroleum and natural gas and are not suitable. The organic matter is decomposed by a series of bacteria in the absence of oxygen and the efficiency of the process is affected by the temperature of the digester, pH, Carbon/Nitrogen ratio, retention time and the presence of substances toxic to the bacteria.  Sewage Sludges have not been included because they are controlled under the Sewage Sludge Matrix, and would not normally be mixed with other organic wastes.  The treatment of industrial waste waters which is largely a remediation process designed to convert effluent to clean water is also not relevant to the feedstock survey.

Inorganics	Source Industrial Activities	In Feedstock
Cadmium	Alloys and Electroplating Industries.  PVC stabiliser.	Paints, pottery, nails, screws, batteries, fungicides
Chromium	Alloys & Stainless Steel. Chemical industry, tanning, pigments	Wood protection, paints, varnish,
Copper	Chemical & electronic industry	Domestic products, piping, pig & poultry fodder, fungicides
Mercury	Mining, coal, combustion, incineration	Pharmaceutical products, thermometers, fungicides
Nickel	Stainless Steel Production, metal industry, NiCd accumulators	Cosmetic products, pigments
Lead	Mostly confined to old industrial activity and materials, not used extensively for new products	Piping, roof materials, batteries
Zinc	Surface Treatment, Galvanising	Batteries, textiles, pharmaceutical industry, paint

Organics	Source Industrial Activities	In Feedstock
PCB (polychlorinated biphenyls)	Was widely used in industry especially in electrical equipment.  Production prohibited in UK in 1984.  Pollution mainly airborne	Found in old paints, plastics, rubber electrical equipment. Persists in paper & cardboard.
Polychlorinated Dibenzodioxins & Dibenzofurans (PCDD/F)	Chemical Industries, (chlorinated compound processes), manufacture of insecticides, herbicides, antiseptics, disinfectants, wood preservatives	Main source is treated wood products, chipboard and leaves/grass from contaminated areas
PAH (Polycyclic aromatic hydrocarbons) - from	Colouring agents, mothballs, wood treatment, refrigerating material, fungicide (paper industry), incomplete combustion of materials, smoke, engine exhaust	Major source is exhaust gases from cars or industry, dissolved in water.  Also tar & asphalt, very persistent, absorbed by plants.
Chlorinated Pesticides, including Lindane, DDT etc	Once widely used in agriculture, now mostly banned, but still present in domestic wastes from gardens	Insecticides, most commonly Lindane, Pyrethroide, Thiabendazole
LAS (linear alkylbenzene sulphonates)	A biodegradable surfactant manufactured for use in cleaning products.   Degrades aerobically	Household detergents, powders, soaps, rinsing and cleaning agents
NPE (Nonylphenols)	Used in detergent manufacture for industry and households.  Degrades aerobically.	Detergents and washing powders
DEHP (2—ethyexyl) phthalate	A plasticiser in construction and packaging industries and PVC, resin manufacture, medical products	Foils, floor mats, lacquers, plastic bags

External Controls for Feedstock quality

Waste Collection Organisation is responsible for multi-source collection, education, training, feedstock test & delivery to AD facility

Single producer with internal process controls and feedstock tests and a atransport contract for deelivery of the biodegradable waste

 

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