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Electro-chemical treatment of fresh animal manure for reducing environment and health risk (electro project)

Contract nr: FAIR-CT97-3506
Project nr: 3506
Project type: SC
Starting date: 01/06/1998
Duration: 36 months
Total cost: 600,000 EUR
EC Contribution: 600,000 EUR
Scientific Officer: Lucia PENA ALBERDI
Research topic: Animal health
Acronym: ELECTRO


Animal wastes are an important source of fertilisers but are also potential chemical, microbiological and air pollutants. The presence of faecal bacteria and the production of malodorous compounds during storage can be a cause of concern in populated areas.

In the last decade, numerous studies have been published on processes leading to a reduction in pollution from animal wastes. Simple and complex techniques have been employed: lagooning, anaerobic digestion with or without energy recovery, aeration, composting, etc. In the past, some efforts had been made to use an electric current to treat manure, but they required large amounts of electrical energy. This means that, in comparison to other treatment (e.g. aeration) there is no advantage.
Recently it was demonstrated that, under laboratory and practical conditions, treatment applied during storage with very low currents and copper electrodes leads to good results for the reduction of odour, better homogenisation and a reduction of the pathogens in the manure both during storage and spreading. On the other hand, not all of the 400 plants currently working are really effective, and the cause of this erratic behaviour is not known.

The overall goal of the investigation is to study the phenomena of very low electric fields obtained by introducing different electrodes into stored manure, in order to design a technology for emission reduction and hygienic control of manure before disposal into the environment.
The intermediate objectives are:

1) to study the electro-chemical phenomenon;
2) to design a technology to reduce ammonia and other noxious gas emissions, and the deodorisation and hygienic control of manure before disposal;
3) to analyse the key factors for process effectiveness;
4) to set-up new bio-indicator parameters to monitor the electro-chemical treatment applied to manure, with particular reference to pathogens;
5) to elucidate the role of the electric effect, metal ions, toxic compounds etc. on the metabolic activities of microflora related to odours release;
6) to assess the technical and economic feasibility of the process.

The project will be developed by partners in two geographical areas, characterised by different climatic conditions (Mediterranean area and continental area). For the electro project implementation the following steps are envisaged:

1) manure characterisation: the most important chemical and microbiological characteristics will be considered to compare manure of different origin and to monitor the electrochemical process;
2) mechanisms of action: in-depth research on the effect of the electro-chemical process on micro-organism metabolism will be carried out - the interaction of surviving pathogens with metal-ions, formation of toxic compounds, etc. will be considered;
3) bio-monitoring: the new parameters will be compared with those obtained by traditional biological indicators as microbial counts and chemical parameters;
4) monitoring of working parameters, emission and hygienic quality of the air in laboratory, pilot and medium-scale plants in order to optimise the process and to prove its effectiveness;
5) technical and economical feasibility - during the experimentation the energetic needs will be carefully evaluated.
Keywords: animal manure-electrochemical treatment-phatogens-emissions-ammonia-odours.

Current situation/results (first year):
During the first year of the project, the tasks concerning the chemical and microbiological characterisation and the laboratory experiments have been developed. In particular, the chemical and microbiological methods have been discussed and defined both for manure characterisation and for the monitoring of the electrochemical treatment effects; the laboratories and the experimental equipment have been prepared; the analyses of microbial metabolism and odour development, effects on pathogens, biomonitoring parameters and effects on fly development have been started, and are almost completed.

The control units for electrochemical treatment at pilot scale have been designed and assembled; they are ready to operate.
Moreover, in order to create a sound background, specific literature researches have been carried out concerning environmental problems related to animal manure management, electrochemical treatments and their chemical and microbiological effects.

The manure characterisation methods have been precisely defined and described. The physical and chemical parameters considered are: pH, conductivity, total solids, volatile solids, C.O.D., total nitrogen, ammonia nitrogen, nitrates, nitrites, total phosphorus, chloride, copper and zinc. The microbiological parameters considered are: aerobic heterotrophic bacteria, anaerobic heterotrophic bacteria, anaerobic cellulolytic bacteria, anaerobic proteolytic bacteria, spore-forming bacteria, anaerobic ammonifying microorganisms, salmonella, coliform group, total aerobic bacteria, total anaerobic bacteria, gram-negative, aerobic bacteria, enterococcus spp., clostridium perfringens.

During the first year, several experimental tests have been carried out at a micro-scale (5 ml electrolytic cells), at a very small-scale (1 - 5 l electrolytic cells) and at a lab-scale (50 l electrolytic tanks). Even if several experimental results are still under elaboration, the following preliminary results can be underlined.
The inhibitory effect on E. coli activity in nutrient broth could be due to the Cu++ ions produced by the electrolytic process.

The copper-copper electrode couple, in presence of current intensity of 20 mA and in nutrient broth, determines the same effects on the E. coli growth and metabolic activity as the graphite-copper electrode couple.
As regards the total electrode weight loss in nutrient broth, the release of metal ions from the copper-copper electrode couple was the same percentage as that one from graphite-copper electrodes; this means that the quantity of copper "loss" in the nutrient medium from the copper-copper electrode couple in terms of mg Cu, was about twice that observed of Cu loss in the medium from the graphite-copper electrodes.

Making a comparison between treated (electrolysis) and untreated NaCl medium, no bacterial growth was observed in the treated solution after three weeks, whereas only a slight decrease in bacterial concentration occurred in the untreated solution. Analysing these results together with those observed in a NaCl solution where a chemical dissolution of CuSO4 occurred, it is possible to hypothesise that the copper ion lethal effect on E. coli is increased by the effects of low electric fields.

ATP content and multi-enzymatic activities seem to be equally good indicators of electrochemical treatment microbial effects.
In electrolytic treated tanks a large reduction in fly larvae population was observed. This reduction could result from two effects. Firstly, it is assumed that the reduction is caused by the electrical field; secondly, it could result from the reduction or the absence of a swimming layer in the electrochemical treated unit.


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