R.W. Melse

Sustainable intensive livestock production demands manure and exhaust air treatment technologies

Intensive livestock production is connected with a number of environmental effects, including discharges to soils and surface waters and emissions to the atmosphere. In areas with a high livestock density the low availability of nearby arable land, together with the preferred use of chemical fertilizer by arable farmers, results in high off-farm disposal costs for manure. Furthermore, ammonia abatement technologies, such as treatment of exhaust air, are important as ammonia emissions may account up to a quarter of the total nitrogen flux. Firstly, the paper describes and discusses the development of manure treatment in the Netherlands since the 1970s. Manure treatment processes that result in products that compete with and replace the use of chemical fertilizers can (partly) close the nutrient cycle again. From this point of view aerobic treatment of manure (nitrification/denitrification) can not be considered sustainable as nitrogen is taken out of the cycle at high environmental costs. Secondly, the state-of-the-art of techniques for treatment of exhaust air is presented. Besides ammonia, application of air treatment may also reduce environmental emissions of odour and particulate matter (dust). Both manure treatment and treatment of exhaust air are considered essential for sustainable livestock operations in areas with a high livestock density.

Air treatment techniques for abatement of emissions from intensive livestock production

Intensive livestock production is connected with a number of environmental effects, including emissions of ammonia (NH3), greenhouse gases (CH4 and N2O), odour, and particulate matter (PM10 and PM2.5). Possible strategies for emission reduction include feed management, adaptation of housing design, and, in case of mechanically ventilated animal houses, the application of end-of-pipe air treatment, viz acid scrubbers and bioscrubbers. Air treatment techniques can achieve very high emission reductions (up to 100% ammonia removal for acid scrubbers). Furthermore, air treatment offers the possibility to achieve removal of not just one compound but of a combined removal of a variety of pollutants (ammonia, odour and particulate matter) at the same time. The successful application of scrubbers is of increasing impor- tance as intensive livestock operations have to comply with ever stricter regulations and emission limits. Research is needed to address topics such as reduction of costs (both investment and operational costs), improvement of process con- trol to guarantee stable removal efficiencies, decrease of N2O production in bioscrubbers, and increase of odour removal efficiency. 1 Ammonia emission contributes minimally to odour emission because the odour threshold of ammonia is relatively high, viz 5 ppm (3), which is un- likely to be found outside animal houses. Therefore, emission of ammonia and odour are discussed as separate issues.

Nitrous oxide (N2O) emissions from biotrickling filters used for ammonia removal at livestock facilities

Recently several manufacturers of nitrifying biotrickling filters for ammonia (NH3) removal at animal houses have started to add a denitrification step to the installation, aiming to reduce the amount of discharge water by conversion of NH3 to nitrogen gas (N2). The aim of this research was to quantify the possible formation of nitrous oxide (N2O), which is a potent greenhouse gas, in three of these farm-scale installations. Furthermore, the removal efficiency of NH3 and odor was determined. All installations were successful in reducing the amount of discharge water. The average NH3 removal efficiency for the three locations was 85, 71 and 86%, respectively. However, a significant part of the NH3 removed from the inlet air was not converted to N2 but to N2O, which is a potent greenhouse gas. The part of the inlet NH3-N that was converted to N2O-N amounted to 17, 66 and 24%, respectively. The high N2O production might have been caused by a too low scarcity of biodegradable carbon/N ratio for complete denitrification. The average odor removal efficiency was 21, 32 and 48%, respectively. Further research is necessary to explore how process conditions can be adjusted and controlled in order to reduce the production and emission of N2O from these types of systems.

Evaluation of the NH3 Removal Efficiency of an Acid Packed Bed Scrubber Using Two Methods: A Case Study in a Pig Facility

The use of air cleaning systems to reduce ammonia emissions from animal houses is increasing. These systems are normally used in order to comply with local or national regulations of ammonia emission. Therefore, accurate determination of the proportion of ammonia being removed by these systems is crucial. There are two main methods available to measure ammonia removal efficiency of scrubbers: air balance (based on the measurement of ammonia concentrations in air) and combined water-air balance (in which it is also necessary to determine the amount of nitrogen recovered in the liquid phase). The first method is simpler to establish, while the second method might provide deeper information about the processes occurring. The main aim of this work was to assess, in terms of the variability of the results, the use of these two methods to evaluate the efficiency of an acid packed bed scrubber on a pig farm. An acid packed bed scrubber (70% NH3 removal) was monitored during ten complete 24 h cycles for ammonia concentrations, airflow rates, and nitrogen accumulation in the acid solution basin. The average efficiency calculated using the air balance method was 71% (±4%), close to the design value of 70%, while the average efficiency when using the combined water-air balance method was 255% (±53%). The accumulation and precipitation of ammonium salts in the packing material seem to be the main cause of the high variability and inaccuracy of the combined water-air balance method observed for this type of scrubber. According to these results, it is recommended to use the air balance method when determining the ammonia removal efficiency for acid packed bed scrubbers similar to the one studied here. According to the variability of the results observed in this work, at least 24 measurement days are needed in order to keep the relative error below 5% when using the air balance method to determine the ammonia removal efficiency of an acid packed bed scrubber.

Multi-Pollutant and One-Stage Scrubbers for Removal of Ammonia, Odor, and Particulate Matter from Animal House Exhaust Air

In several European countries, acid scrubbers and bio-scrubbers are off-the-shelf techniques for effective removal of ammonia from exhaust air from animal houses and, to a lesser extent, for odor. The number of operating air scrubbers at livestock operations in the Netherlands in 2008 is estimated to clean the air of approximately 10 percent of the pigs produced nationwide. Currently, a new generation of so-called multi-pollutant air scrubbers are developed for intensive livestock production that mitigates emissions of both ammonia, odor and PM10/2.5. A research and implementation program has been set up by the Dutch government that aims to stimulate the development and introduction of multi-pollutant air scrubbers The objectives of this paper are to give an overview of technical principles applied in the current generation of scrubbers for livestock operation, and present results from research on one-stage scrubbers applied in pig and poultry production and preliminary results of the Dutch research program with regard to removal efficiencies and operational parameters of multi-pollutant scrubbers. Results are presented from tests of an acid scrubber developed for pig and poultry facilities. Mean ammonia removal performance on two poultry and two pig locations were all higher than 90%, means of odor removal varied between 26 and 64%. The first preliminary results of multi-pollutant scrubbers are shown. Future measurements will be carried out in the coming two years in order to get reliable data on long-term performance of the multi-pollutant scrubber systems.

CONCENTRATION OF URINE FROM FATTENERS COMBINED WITH AMMONIA REMOVAL BY SCRUBBING EXHAUST AIR OF A PIG HOUSE

In the Dutch Hercules project feces and urine from pigs are collected separately and treated in two processes: feces are composted and urine is concentrated by water evaporation. Water unsaturated exhaust air from the pig house is used for evaporation in a packed bed scrubber. The urine is acidified with nitric acid to scrub ammonia from the air. In this way a concentrated N/K fertilizer is produced from urine and ammonia is removed from the pig house exhaust air. Experiments were conducted using a pilot scale packed bed scrubber in an experimental pig house. The ammonia scrubbing efficiency and the evaporation rate were determined during one pig fattening round of 112 days. The average composition of the collected pig urine was 4.4 g nitrogen/kg, 6.6 g potassium/kg and 0.03 g phosphorus/kg. The volume of the urine was reduced by a factor 6-7 resulting in a concentrate composition of 91.3 g/kg total nitrogen (including nitrogen added as nitric acid), 46.5 g/kg potassium and 0.2 g/kg phosphorus. The mean evaporation rate was 28 kg/day at inlet air conditions of 74% relative humidity and a temperature of 19°C. The inlet air of the scrubber was more humid (74% instead of 60%) than expected. This resulted in a evaporation rate that was below expectations. The ammonia scrubbing efficiency was determined 5 times and ranged from 68 to 95%. The efficiency decreased at higher salt concentrations of the urine.

StalSens-Oren: meetsystemen voor bedrijfs-monitoring van emissies in de veehouderij : deskstudie naar de mogelijkheden voor directe emissieregistratie

Regulations on emissions of ammonia, fine dust and odour from livestock barns are based on emission factors of specified housing systems derived from field testing programmes of prototypes. Compliance with emission regulations is verified by inspection on the presence of specified housing systems on farms. An alternative regulatory approach is to rely on a farm based monitoring system that allows farmers to comply with a specified emission target by mitigation measures of their own choice. To enable this approach the development of a reliable and cost affordable farm monitoring system is needed. This report provides an overview of current technical options and perspectives for development, as well as a list of requirements that farm monitoring systems for emissions would need to meet.

Evaluatie geurverwijdering door luchtwassystemen bij stallen: Deel 1: Oriënterend onderzoek naar werking gecombineerde luchtwassers en verschillen tussen geurlaboratoria

In deze studie is de geurverwijdering gemeten bij twee typen combi-wassers op elk twee bedrijfslocaties. De luchtwassers waren achter een varkensstal geschakeld. Per bedrijfslocatie zijn in de zomer van 2016 zes geurrendementsmetingen uitgevoerd door een Duits en een Nederlands geurlaboratorium. Uit de studie blijkt dat de bemeten vier combi-wassers aanzienlijk lagere geurrendementen realiseerden dan de waarden waarvan uitgegaan wordt in de Regeling geurhinder en veehouderij. Daarnaast bleek dat er systematische verschillen bestaan tussen de geurconcentraties die door beide geurlaboratoria werden gemeten.

Emissie van stikstofverbindingen uit luchtwassers met biologische wasstap

In de regel wordt aangenomen dat in luchtwassers met een biologische behandelingsstap ammoniak uit stallucht wordt omgezet in nitraat en nitriet, dat vervolgens met het spuiwater wordt afgevoerd. Er zijn echter aanwijzingen dat onder bepaalde condities (grote) hoeveelheden andere gasvormige stikstofverbindingen kunnen ontstaan en emitteren. Uit de steekproef die is uitgevoerd, blijkt dat bij biologische luchtwassers met een lage pH (<6,5) grote hoeveelheden stikstofoxyden (NOy) kunnen ontwijken naar de lucht. Voor dergelijk luchtwassers is de netto stikstofverwijdering veel lager dan de ammoniakverwijdering---In a biotrickling filter treating animal house exhaust air, ammonia is usually converted to dissolved nitrite and nitrate and subsequently removed with the discharge water. However, under certain operating conditions other types of gaseous nitrogen compounds may be emitted to the air. From the survey that was conducted it follows that at low pH values (<6.5) large amounts of gaseous nitrogen oxides (NOy) may be emitted from biotrickling filters. As a result, the net nitrogen removal of these scrubbers is much lower than the ammonia removal efficiency

Fine Dust (Pm10) Removal by Air Scrubbers Treating Animal House Exhaust Air

Air scrubbers (mainly acid scrubbers and biotrickling filter) are commonly used for removal of ammonia and odor from ventilation air of animal houses in The Netherlands in order to comply with current regulations. Besides, air scrubbers remove a large part of the coarse dust and will to some extent also remove fine dust (PM10). In this paper the state-of-art of scrubber application at animal houses is reviewed with regard to ammonia and odor removal. Next, the results are presented of a measurement program where PM10 removal of farm-scale air scrubbers was monitored year round. It was found that scrubbers with at high air contact time (Empty Bed Residence Time (EBRT) > 7.5 s) can achieve high PM10 removal efficiencies (on average 68%). At low air contact times (EBRT < 7.5 s), however, efficiencies were much lower (on average 44%). This might be explained by the phenomenon that the diameter of dust particles increases when passing through the scrubber, resulting in higher removal efficiency at higher contact time. However, further theoretical and experimental research is necessary to understand the wide range of PM10 removal efficiencies that was find at low contact times.