**Biodegradation of Ammonia in Biofiltration Systems: Changes of Metabolic Products and Microbial Communities**

Yiu Fai Tsang, Ya‐nan Wang, Huawei Wang, Yi Yang, Yuanhui Zhang and Hong Chua

Additional information is available at the end of the chapter

http://dx.doi.org/10.5772/intechopen.68155

#### **Abstract**

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In the first stage, the feasibility of using the waste materials from coal power plants (i.e., coal slag) and landscapes (i.e., wood chip and compost) as packing media in various biofiltration systems for ammonia (NH<sup>3</sup> ) removal was investigated. In the second stage, the optimized biotrickling system packed with coal slag was employed to investigate the effects of inlet concentration on NH<sup>3</sup> treatment performance. A complete NH<sup>3</sup> removal was achieved at concentrations of up to 250 ppm at an empty bed retention time of as low as 8 s, which is shorter than most previously reported biofiltration systems. Results of metabolic product analysis indicated that half of introduced NH<sup>3</sup> was oxidized to nitrate and the rest was converted to ammonium ion at low loadings, while nitrite and ammo‐ nium ions predominate at high loadings. A bacterial community shift was observed with regard to the loading rates and pH conditions. In addition, there were no common oper‐ ating problems, such as clogging and compaction, in the operation for more than 1 year.

**Keywords:** biofilter, biotrickling filter, ammonia removal, nitrogen mass balance, microbial community

### **1. Introduction**

Ammonia is characterized as a colorless, toxic, reactive, and corrosive gaseous pollutant with a strong and repulsive smell [1]. NH<sup>3</sup> is emitted as a by‐product of different industrial pro‐ cesses, such as wastewater treatment, composting, livestock production, and petrochemical refining [2, 3]. Its emission causes significant odor nuisance, health impacts, and environmen‐ tal problems. It has been reported that exposure to NH<sup>3</sup> above 1 ppm could cause nausea,

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headaches, bronchial tract irritation, and burning sensation in the eyes and skin [4, 5]. It is crucial to control NH<sup>3</sup> emission to protect public health and the environment.

The conventional ammonia treatment methods are based on physical and chemical processes, such as adsorption, scrubbing, and chemical oxidation. Unfortunately, these are expensive and produce secondary waste that may require further treatment or disposal, thereby creat‐ ing additional environmental problems [6, 7]. Biofiltration is an emerging technology for the control of odor and ammonia from contaminated air streams [8–10]. Studies suggest that com‐ post‐based biofilters are the most cost‐effective for low‐concentration ammonia removal in the agricultural industry due to their low operating and maintenance costs. Other supplementary materials (e.g., wood chips) are commonly added to reduce pressure drop and provide a solid‐phase buffer [8]. The primary mechanism of biofiltration is the heterogeneous biochemi‐ cal process controlled by either mass transfer or biochemical reaction or both. Pollutants are transferred from the air to the water layer or to the biofilm attached on the packing media by adsorption or absorption. The sorbed contaminants in the biofilm are degraded by microor‐ ganisms into carbon dioxide, water, biomass, and energy [6, 7].

The main functions of the packing media are to provide contact between the gaseous con‐ taminants and the active biofilm and to distribute water and nutrients on the packing surface [8, 11]. Biofilter performance and operating cost are affected by the media characteristics, such as surface area, mechanical properties, buffer capacity, nutrient availability, porosity, and water retention capacity, hence providing an ideal environment for microbial growth [10, 11]. Therefore, the selection of suitable supporting materials and operating mode is an important aspect of a successful biofiltration process.

There are three general classifications of media, namely, natural, inert, and synthetic. Natural materials, including peat, soil, and compost, are generally chosen as biofilter media because they are inexpensive and have a wide diversity of indigenous microorganisms [11, 12]. In addition, several research studies have revealed that natural packing materials provide supe‐ rior performance in ammonia treatment [8, 13]. Nonetheless, natural‐based biofilters are often plagued by common operating problems, such as compaction and decomposition, hence resulting in high pressure drop and air channeling. Common inert materials used in biofiltra‐ tion include glass beads, perlite, and porous ceramics. Inert materials are difficult to compact. Moreover, they maintain a stable composition during long‐term operation. Consequently, they could be used as an alternative to natural media [11]. However, their wide application is stifled due to high material costs and nutrient deficiency.

Different natural and inert packing materials have been successfully applied in biofiltra‐ tion systems [10, 14, 15]. Likewise, extensive studies have focused on the selection of filter materials and on the optimization of reactor design and operating criteria to obtain efficient ammonia removal in biofiltration systems. However, it is difficult to evaluate the efficiency of various filter materials, because the simultaneous comparison of natural and inert packing media has not been clearly determined under the same conditions. In addition, there are only limited studies on inert packing materials and trickling operations. In our previous study, an attached growth bioreactor packed with coal slag was successfully utilized for domestic wastewater treatment both in lab‐ and pilot‐scale experiments, indicating that coal slag is a viable supporting material for biofilm attachment and long‐term operation [16–18]. The relatively high adsorption capacity of coal slag is also an advantage in the biotrickling filter.

The aim of this study is to determine the feasibility of using recycled wastes as packing media in biofiltration systems for ammonia removal. Potential packing materials were characterized and selected for further investigation, and different operating modes of reactors, namely, bio‐ filter and biotrickling reactor, were also evaluated in terms of ammonia elimination capaci‐ ties. The removal mechanisms and the inhibitory effects were also investigated through the mass balance analysis.
