Robert W. Sneath

A farm-scale study on the use of clinoptilolite zeolite and De-Odorase® for reducing odour and ammonia emissions from broiler houses

Intensive poultry farms are frequently the subject of odour complaints and are also known emitters of ammonia. In this paper an experiment is described which compared the effectiveness of two abatement compounds, clinoptilolite and De-Odorase®, when used in broiler production. Two sites were used which had almost identical buildings, each with two rooms, and the same strain of bird. Clinoptilolite was used on one site and De-Odorase® on the other. Once a week ventilation rate, ammonia concentration and odour concentration were measured, to determine the effects of the additives. We also measured temperature, relative humidity and carbon dioxide concentration to confirm that the control and test rooms had similar micro-climates. In the room treated with clinoptilolite the ammonia concentration was statistically significantly higher than in the control and the total mass of ammonia emitted was 50% greater. In the De-Odorase® experiment the mean ammonia concentration in the treated room in the final week was 38% lower than in the control and the total mass of ammonia emitted from the treated room was 50% lower. There was no statistically significant reduction in the odour concentration or odour emission rate for either of the additives used.

Evaluation of a radial basis function neural network for the determination of wheat quality from electronic nose data

Abstract Odorous contaminants in wheat have been detected using a conducting polymer array. A radial basis function artificial neural network (RBFann) was used to correlate sensor array responses with human grading of off-taints in wheat. Wheat samples moulded by artificial means in the laboratory were used to evaluate the network, operating in quantitative mode, and also to develop strategies for evaluating real samples. Commercial wheat samples were then evaluated using the RBFann as a classifier network with great success, achieving a predictive success of 92.3% with no bad samples misclassified as good in a 40-sample population (24 good, 17 bad) using a training set of 92 samples (72 good, 20 bad).

A farm scale study on the use of De-Odorase® for reducing odour and ammonia emissions from intensive fattening piggeries

Abstract An experiment was mounted at a large fattening piggery in Slovenia, during which different groups each of 600 weaned pigs were housed and grown in different fattening rooms for 60 days (from age 24 days to age 84 days). All rooms were mechanically ventilated and had fully-slatted floors with slurry channels beneath. De-Odorase ® † was added to the diet of the treated groups of pigs at the rates recommended by the suppliers, e.g. for grower feed, 65 g/t. De-Odorase ® was also added daily (3·2 g suspended in 10 l of water) to the upstream ends of the slurry channels. Once a week, the ammonia concentration in the air inside each fattening room was measured at each of four positions, using Drager tubes, and the ventilation rate was computed from the cross-sectional area of each fan outlet and the average velocity of the air emerging from each. Also, air samples were taken from immediately outside three of the fans serving each room, and their odour concentrations were measured by olfactometry. Hence, weekly values of emission rates of both ammonia and odour could be calculated. Ammonia concentration was significantly lower ( P = 0·001) in the De-Odorase ® -treated buildings than in the control buildings. The average reduction in ammonia concentration over a 7 week period was 26%. Ammonia emission rate was also reduced by 26% through the use of the additive. This reduction was significant at P = 0·048. Neither odour concentration nor odour emission rate was significantly reduced through the use of the additive. The additive did not significantly influence the rate of live-weight gain by the pigs.

Continuous aerobic treatment of piggery slurry for odour control scaled up to a farm-size unit

Effective aerobic treatment of piggery slurry was achieved in a continuous farm scale process sited at a small piggery (2000 pigs). The plant design and the operating conditions were based on data obtained from pilot-scale studies with the aim of preventing or reducing odours from pig slurry at a minimum cost. Raw slurry was separated before passing into the main treatment vessel. Aeration was achieved by recirculating of slurry (achieving jet mixing of the tank contents) through a venturi where air was entrained. Aeration was controlled to maintain redox potential between 100 and 200 mV E h . Slurry was added and withdrawn at hourly intervals, to provide nominal residence times of 1, 2 and 4 days. The performance of the aerobic treatment process in terms of COD reduction could be predicted using data from laboratory and pilot-scale experiments. Some allowance could be made for minor feed fluctuations but a more comprehensive model will be necessary for predictions where larger variations occur in operating conditions. Assessments were made of odour quality using dynamic dilution olfactometers for odour strength, and volatile fatty acids (VFA) concentration as an indicator of odour offensiveness. Results indicate that pilot-scale experiments may overestimate by 10–20% what can be achieved with the farm-scale plant. Nitrogen losses were greatest in the 4-day residence time trial with 56% lost in the form of N 2 gas following a nitrification/denitrification process. Conversely, in the short residence time trials, virtually all of the nitrogen was conserved.

An assessment of ways to abate ammonia emissions from UK livestock buildings and waste stores. Part 1: ranking exercise

Abstract The options for abating ammonia emissions from livestock buildings and waste stores under UK conditions have been assessed. There is increasing interest in reducing such emissions, which contribute to long-range atmospheric pollution problems, and which, via subsequent deposition, can also harm sensitive ecosystems. A literature review was first carried out, and a “brainstorm” idea-generating session was held, together leading to lists of feasible abatement approaches: one for each of a range of types of livestock buildings and waste stores. A ranking exercise was then conducted. A set of aspects of each application of each feasible abatement approach was drawn up: the aspects considered included not only capital costs and running costs but also such others as animal welfare, stage of development and knock-on effects. Each aspect of each application of each approach was given a ranking of between 1 (very poor) and 5 (very good). When the aspects of “potential abatement” and “achievable abatement now”, as well as either “capital costs” or “animal welfare”, were weighted by a factor of 5, the “best bet” abatement approaches for livestock buildings were identified as (a) dietary manipulation (for all types), (b) raising the C/N ratio by generous use of bedding (for any buildings based on solid manure), (c) exhaust air cleaning, especially by bioscrubbers (for force-ventilated pig and poultry buildings), (d) oil layers or (e) fixing with acid (for slurry-based piggeries) and (f) drying by ventilation of muck (for any poultry building). For waste stores, the “best bet” abatement approaches were identified as (g) replacing storage with industrial scale processing or (h) with land filling (niche solutions only), (i) dietary manipulation, (j) fixing with acid (slurries only), (k) increasing the surfaces resistance to ammonia volatilisation (by crusts for cattle slurry, but by floating granules for pig slurry), (l) minimising surface area by heap shape (solid manures), and (m) cover sheets (solid manures). For stored poultry manure, the low moisture content allowed good showings by the additional options of (n) drying, and, in the case of poultry manure with litter in certain parts of the UK, (p) sale for combustion in a Non-Fossil Fuel Obligation (NOFFO) power station, the electricity from which commands a higher price than that from a conventional power station. A closer look at the economic consequences of different abatement approaches was taken by means of a mathematical model: this work is reported in a companion paper.

Centrifugation for separating piggery slurry 1. The performance of a decanting centrifuge

Abstract Odour nuisance arising from piggery slurry can be prevented by aeration. The stability of aerobically treated slurry, which is free of offensive odours, increases as the dry matter of the slurry decreases. This paper investigates the performance of a decanting centrifuge as one means of achieving a lower dry matter in piggery slurry. Slurry was centrifuged to show the effects of various operating conditions; 61% of the total solids were removed from slurry of 8% dry matter content wet basis (d.m.) in the form of fibrous solids of 27% d.m. and 43% of the total solids were removed from slurry of 2% d.m. as fibrous solids of 30% d.m. When the raw slurry had 8% d.m., centrifuging reduced the volume needed for liquid storage by 17%. A particle size analysis of the solids which remained in the centrifuged liquid showed that 98% were less than 0·020 mm diameter. This agrees with the predicted maximum size of particle left in the centrifuged liquid. Centrifuged liquid from the dilute slurry contained only 4% of particles greater than the predicted maximum diameter of 0·012 mm.

Development of a perimeter odor monitoring system for landfill sites

A need exists for instrumentation capable of continuous measurement of gas and odor emission from the perimeter of a landfill site. Current practice is to manually use a flame ionization detector. Instruments based on an array of MOS gas sensors were developed and placed on the perimeter of a landfill site, functioning as point monitoring systems, using methane as a surrogate for odor emission. The single-point instrument (SPEMMI) proved to be sensitive to methane, with the sensors showing a change in resistance of about 4% for a methane concentration of 50 ppm. On-site measurements showed that, while there was some sensitivity to temperature, it was possible to identify methane emission events. Data analysis techniques using a Savitsky-Golay second order filter show that event detection was possible. The system was operational in the field and was reliable. The use of complementary, n-type and p-type gas sensors, allowed discrimination of gas events from ambient temperature fluctuations.

Automated indirect method of ammonia flux measurement for agriculture: effect of incident wind angle on airflow measurements

Abstract Cost effective, distributed instrumentation arrays have to be developed to realise a robust automated ammonia flux measurement system suitable for use at the periphery of naturally ventilated livestock buildings. The new system is designed to permit the calculation of ammonia flux indirectly from measurements of ammonia concentration, using conducting polymer sensors, and wind speed with direction, via a commercially available airflow sensor. This paper discusses the problems associated with calculating external wind speed from measurement of airflow rates within a fixed sampler tube. It is necessary to be able to compensate for anomalous flow regimes within the sampler system, which can arise from changes to the external wind direction. Wind conditions, across the site of interest, should be faithfully recorded throughout the experiment, otherwise models based upon the acquired data may be unrealistic.

An assessment of ways to abate ammonia emissions from livestock buildings and waste stores. Part 2: cost modelling

The economic consequences of different ammonia abatement approaches, used either singly or in combination, have been examined by means of a specially developed mathematical model called Sectoral Analysis of Livestock Ammonia Abatement Model (SALAAM). SALAAM basically uses a “process-based” approach, characterising livestock waste management as a cascading system in which flows of Total Ammoniacal or Available Nitrogen (TAN) through different types of system, and through different stages of waste management (e.g. housing, storage, application to land), are linked into an overall flow network. This allows individual calculation of ammonia emissions from different parts of the waste management process, and systematic analysis of the effects of changes in the system (e.g. through implementation of abatement measures) by adjusting flow volumes within each pathway. The model was used to carry out three separate exercises: (a) to determine the economic value of individual abatement measures, (b) to calculate maximum feasible reductions, and (c) to estimate potential abatements in relation to the sector livestock values. The results from SALAAM were as follows. For (a), the ranked unit cost (£/kg NH3 abated) followed an exponential curve, the overall range of unit cost, in the above units, being from zero to many hundreds. The approaches of dietary manipulation, individual feeding, industrial scale processing, fixing with acid and animal breeding showed up well, with low unit costs in each of several sectors. For (b), the maximum feasible reduction was rather lower for the cattle industry (at just over 40%) than for the pig and poultry industries (at around 70%). For (c) the potential emission reductions at an expenditure level of 10% of the annual value per animal place were calculated. With pigs and poultry, abatements close to the maximum feasible reduction were achievable at an expenditure of not more than 10% of the annual value, but with cattle, especially non-dairy, much higher percentages of the annual value would need to be expended to approach the maximum feasible reduction. There was general agreement between the results from these modelling techniques and those from a complementary ranking technique, but no one single approach is likely to solve all building and store abatement problems. Rather, it will be necessary to deploy, on a national scale, a combination of approaches, each of which has been carefully selected from amongst those identified as promising during this study. The results, both of this modelling work and of the complementary ranking exercise, reported in a companion paper, would be made more robust if stronger and more complete cost data than those which have so far been available could be sought out and/or estimated for the various different abatement approaches identified.

Solid State Chemical Sensors: Technologies and Applications

The agricultural industry needs to be more accountable with regard to environmental pollution. This has arisen because the adoption of increasingly intensive farming methods in agriculture, with the associated production of significant quantities of solid and gaseous waste emissions that has, in recent years, been linked to adverse environmental change. Solid state chemical sensors are highly desirable, but available technology still lacks robustness for use in the agricultural field. This paper reviews sensing, sampling and measurement technology applicable to real-time monitoring of gaseous fluxes.