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This study presents the start-up and 1-year performance study of two full-scale biotrickling filters or biological air scrubbers at a pig fattening facility in terms of ammonia removal and nitrous oxide production. Two newly-built multi-stage biotrickling filters were continuously monitored for these gases and for washing water characteristics. Although pH and electrical conductivity in the washing water are used in practice as a cheap and easy way to monitor the ammonia removal efficiency of biotrickling filters at pig housing facilities, it was shown that the relation between these variables is not always straightforward. Setting up a nitrogen balance over both biotrickling filters suggested denitrification activity. Additionally, the effect of inoculation with activated sludge of a wastewater treatment plant was investigated by inoculation of one of the two biotrickling filters. The inoculated biotrickling filter showed a fast start-up of nitrification and hardly any nitrite accumulation in the washing water. The ammonia removal efficiency was higher and the nitrous oxide production was slightly lower in the inoculated biotrickling filter compared to the non-inoculated. • Inoculated biotrickling filter starts up faster and has less nitrite accumulation. • Nitrite accumulation induces higher nitrous oxide emissions. • High ammonia removal can be reached even in extreme conditions. • Total nitrogen content can be estimated using a validated EC correlation. • Nitrogen mass balance suggests a significant denitrification amount. [ABSTRACT FROM AUTHOR]

The global intensification of livestock production resulted in potentially higher emissions of ammonia, odour, particulate matter (PM) and greenhouse gases (nitrous oxide and methane). Air scrubbers and biofilters were introduced as a low ammonia emission housing technique. However, regulations with regard to the use of air scrubbers changed, including also removal efficiencies for odour and PM besides ammonia. In practice however, the required removal efficiencies for these pollutants are not always obtained, indicating the need of process optimisation in terms of process design and/or operation. When optimising air scrubbers, it is argued and recommended to anticipate the growing attention towards greenhouse gases, such as methane and nitrous oxide, which are present in exhaust air from animal housing facilities. However up till now, very little is known about the behaviour of greenhouse gases in air scrubbers and biofilters. Moreover, the formation of nitrous oxide in (biological) air scrubbing systems cannot be excluded. This contribution summarises the state-of-the-art of air scrubbers and biofilters for the reduction of emissions of ammonia, odour, nitrous oxide, methane and fine dust and points out perspectives for process optimisation in terms of design and control. The air and liquid flow configuration, packing dimensions and packing material should be carefully considered. Control options for water flow rate, water discharge and acid dosage need to be optimised. Dosage of apolar solvents and inoculation of the packing material can be innovative control options to achieve a better removal of less water-soluble components. [ABSTRACT FROM AUTHOR]

Farm-scale anaerobic digestion is increasingly regarded as a greenhouse gas emission reduction measure. To get a full picture of its emission reduction potential, greenhouse gas emissions from digestate storage need to be assessed. This work quantifies methane (CH 4) and nitrous oxide (N 2 O) emissions from farm-scale mono-digested dairy manure by continuous monitoring in an on-site digestate storage for three months, in autumn. A dedicated sampling method coupled with an on-line gas phase analyser was developed to enable continuous measurements over longer time periods. The proposed method was a refinement of existing closed chamber approaches and involved repeated sampling cycles, including a gas accumulation phase from which the emission rate was quantified. Daily average methane emissions per stored digestate volume varied from 4.6 to 14 g m−3 d−1, equivalent to 3.9 to 8.2% of the methane produced in the digester. Daily average nitrous oxide emissions varied from 0.004 to 0.13 g m−3 d−1. The total emission ranged between 170 and 478 g [CO 2,eq. m−3 d−1, up to 10% of which was attributed to nitrous oxide. Both methane and nitrous oxide emissions increased for a larger stored digestate volume and a higher temperature. The system under study was simulated through an anaerobic digestion model, taking into account prevailing operating conditions in the digester and digestate storage. Substrate-specific input values were identified by analysing the fresh dairy manure and digestate. The hydrolysis constant and gas–liquid transfer coefficient were estimated at 0.21 d−1 and 0.003 d−1, respectively, for simulation results to match experimentally observed methane emission values. • First long-term monitoring of CH 4 and N 2 O emitted by farm-scale mono-digested manure. • Refinement of closed chamber method for continuous, on-line emission measurements. • A larger stored digestate volume and a higher temperature both resulted in more emissions. • Determination of dairy manure composition in terms of carbohydrates, proteins and lipids. • Model calibration by comparing experimentally measured data to simulation results. [ABSTRACT FROM AUTHOR]

A mechanistic model for ammonia removal in a countercurrent biological air scrubber was set up. This model was used to study the effect of the influent characteristics – air temperature, ventilation rate and ammonia load, on ammonia removal efficiency. Besides mass balances of the components participating in the biological conversions, the water mass balance and the heat balance were considered. The effects of the pH and the concentration of the nitrogen components on the driving force for mass transfer were examined. The model output was compared against experimental data from a pig housing facility. Simulations were performed to assess the usefulness of pH control and to investigate the effect of inflow air conditions on the ammonia removal efficiency. The study found out that although pH control affected the nitrogen component distribution in the washing water, it hardly affected the ammonia removal efficiency. Thus, pH control for biological air scrubbers is not recommended in practice, however, an on/off pH control system adding only acid at critical moments (pH above 7.5) could be considered. The variations in the ammonia removal efficiency are mainly caused by a changing ventilation rate rather than air temperature fluctuations or ammonia load. • A mechanistic model for a biotrickling filter for ammonia removal was developed. • pH control affected the nitrogen component distribution in the washing water. • Changing ventilation rate mainly caused variations in ammonia removal efficiency. • Simulation results agreed with experimental data from a pig housing facility. [ABSTRACT FROM AUTHOR]

An anaerobic digestion model was set up and applied to estimate desired methane production in the form of biogas as well as unwanted methane emissions associated with farm-scale digestion of manure. The generally accepted Anaerobic Digestion Model No. 1 was simplified assuming that hydrolysis is rate-limiting during anaerobic digestion of manure, mainly consisting of non-readily biodegradable compounds. Simulations were performed to demonstrate the effect of temperature and retention time on methane emissions resulting from long-term manure and digestate storage. Moreover, the overall carbon footprint of several manure management scenarios for Flemish dairy farms was assessed based on model simulations and literature data. The scenarios assessed, differed in the possible presence of a digester as well as in the manure collection and storage method. A reduction in methane emissions was achieved for lower manure storage temperatures (through external storage) and by decreasing the stored manure volume and thus the storage time before (controlled) anaerobic digestion. At the same time, feeding fresh manure induced an increased methane production in the digester. The lowest carbon footprint could be achieved on dairy farms with fresh manure collection by a manure scraper, followed by controlled digestion and storage of the digestate in a gas-tight tank, located outside. The controlled digestion must take place in a properly managed and correctly dimensioned reactor as high digester methane losses and low digester retention times increase the carbon footprint significantly. • A fit-for-purpose model was set up to estimate methane emissions from manure digestion. • Manure volume and temperature are key variables in methane emission quantification. • Lower temperatures slowed down the rate-limiting hydrolysis process. • Reducing open storage time resulted in higher biogas production and less emissions. • An Excel tool is provided to calculate the carbon footprint of manure digestion farms. [ABSTRACT FROM AUTHOR]

Determining ammonia emission factors (EF) for fattening pig facilities is important from both a regulatory and a research point of view. However, measurements to determine an EF can be time consuming and costly. Several reduced sampling strategies were developed in the past to reduce the costs and measuring time, by taking into account parameters that influence NH 3 emissions. A methodology to evaluate the precision and accuracy of estimated EFs solely as a function of the sampling frequency and strategy is demonstrated. This evaluation was done by using two long-term, high frequency datasets which both contained measurements during two consecutive pig fattening periods. These datasets were subjected to simulated sampling strategies. Long-term, low-frequency grab sampling proved to be more accurate than short-term monitoring. Repetitive short-term sampling events result in increased precision, but as this entails higher investment in time and money it is imperative to strike the balance between desired precision and available resources. A method to help as set guidelines to decide upon the number of short-term sampling events or the length of a long-term, low-frequency monitoring strategy is presented. [ABSTRACT FROM AUTHOR]