Hydrogen sulfide and odor removal by field-scale biotrickling filters: influence of seasonal variations of load and temperature

Wastewater Treatment Plants as a Source of Malodorous Substances Hazardous to Health, Including a Case Study from Poland

Using Poland as an example, it was shown that 41.6% of the requests for intervention in 2016-2021 by Environmental Protection Inspections were related to odour nuisance. Further analysis of the statistical data confirmed that approximately 5.4% of wastewater treatment plants in the group of municipal facilities were subject to complaints. Detailed identification of the subject of odour nuisance at wastewater treatment plants identified hydrogen sulphide (H₂S), ammonia (NH₃) and volatile organic compounds (VOCs) as the most common malodorous substances within these facilities. Moreover, the concentrations of hydrogen sulphide and ammonia exceed the reference values for some substances in the air (0.02 mg/m³ for H₂S and 0.4 mg/m³ for NH₃). A thorough assessment of the properties of these substances made it clear that even in small concentrations they have a negative impact on the human body and the environment, and their degree of nuisance is described as high. In the two WWTPs analysed in Poland (WWTP 1 and WWTP 2), hydrogen sulphide concentrations were in the range of 0-41.86 mg/m³ (Long-Term Exposure Limit for H₂S is 7.0 mg/m³), ammonia 0-1.43 mg/m³ and VOCs 0.60-134.79 ppm. The values recognised for H₂S cause lacrimation, coughing, olfactory impairment, psychomotor agitation, and swelling of the cornea with photophobia. Recognition of the methods used in practice at WWTPs to reduce and control malodorous emissions indicates the possibility of protecting the environment and human health, but these solutions are ignored in most facilities due to the lack of requirements specified in legislation.

Full-Scale Odor Abatement Technologies in Wastewater Treatment Plants (WWTPs): A Review

The release of air pollutants from the operation of wastewater treatment plants (WWTPs) is often a cause of odor annoyance for the people living in the surrounding area. Odors have been indeed recently classified as atmospheric pollutants and are the main cause of complaints to local authorities. In this context, the implementation of effective treatment solutions is of key importance for urban water cycle management. This work presents a critical review of the state of the art of odor treatment technologies (OTTs) applied in full-scale WWTPs to address this issue. An overview of these technologies is given by discussing their strengths and weaknesses. A sensitivity analysis is presented, by considering land requirements, operational parameters and efficiencies, based on data of full-scale applications. The investment and operating costs have been reviewed with reference to the different OTTs. Biofilters and biotrickling filters represent the two most applied technologies for odor abatement at full-scale plants, due to lower costs and high removal efficiencies. An analysis of the odors emitted by the different wastewater treatment units is reported, with the aim of identifying the principal odor sources. Innovative and sustainable technologies are also presented and discussed, evaluating their potential for full-scale applicability.

Volatile sulfur compound emissions and health risk assessment from an A2/O wastewater treatment plant

Anoxic/anaerobic/oxic (A²/O) wastewater treatment has emerged as a major process for treatment of domestic wastewater. One of the issues with wastewater treatment plants (WWTPs) is that volatile sulfur compounds (VSCs) are discharged from them and pose numerous health risks. This study characterized VSC emissions at the water-air interface and concentrations of ambient air exposure from different treatment units in an A²/O WWTP. AERMOD modeling was used to simulate the atmospheric behaviors of discharged VSCs. Results demonstrated that VSC emission fluxes and exposure concentrations had followed a descending order of pretreatment>biological treatment>advanced treatment. Emissions were affected by sulfate concentrations and chemical oxygen demand in the wastewater, and control strategies based on these values were proposed. The AERMOD results indicated that the majority of the total hydrogen sulfide (87%) and methyl mercaptan (65%) emissions came from the primary sedimentation tank, while the majority of dimethyl sulfide (81%), carbon disulfide (84%), and dimethyl disulfide (93%) were emitted from the oxic area. MT and DMS were the main odorous components of the VSCs in ambient air based on the indicator of odor activity values. Noncancer health risks, determined by having a hazard quotient >1, of the measured VSCs were beyond acceptable limits. Overall, efforts should be made to minimize noncancer health risks as individuals are exposed to VSCs not only in treatment units but also in areas surrounding WWTPs.

Treatment of discontinuous emission of sewage sludge odours by a full scale biotrickling filter with an activated carbon polishing unit

A SULPHUS^TM biotrickling filter (BTF) and an ACTUS^TM polishing activated carbon filter (ACF) were used at a wastewater treatment plant to treat 2,432 m³·h^-1 of air extracted from sewage sludge processes. The project is part of Thames Water's strategy to reduce customer odour impact and, in this case, is designed to achieve a maximum discharge concentration of 1,000 ou_E·m^-3. The odour and hydrogen sulphide concentration in the input air was more influenced by the operation of the sludge holding tank mixers than by ambient temperature. Phosphorus was found to be limiting the performance of the BTF during peak conditions, hence requiring additional nutrient supply. Olfactometry and pollutant measurements demonstrated that during the high rate of change of intermittent odour concentrations the ACF was required to reach compliant stack values. The two stage unit outperformed design criteria, with 139 ou_E·m^-3 measured after 11 months of operation. At peak conditions and even at very low temperatures, the nutrient addition considerably increased the performance of the BTF, extending the time before activated carbon replacement over the one year design time. During baseline operation, the BTF achieved values between 266-1,647 ou_E·m^-3 even during a 6 day irrigation failure of the biofilm.

Removal of H2S pollutant from gasifier syngas by a multistage dual-flow sieve plate column wet scrubber

The objective of this study was to observe the performance of a lab-scale three-stage dual-flow sieve plate column scrubber for hydrogen sulfide (H₂S) gas removal from a gas stream, in which the H₂S concentration was similar to that of gasifier syngas. The tap water was used as scrubbing liquid. The gas and liquid were operated at flow rates in the range of 16.59 × 10^-4-27.65 × 10^-4 Nm³/s and 20.649 × 10^-6-48.183 × 10^-6 m³/s, respectively. The effects of gas and liquid flow rates on the percentage removal of H₂S were studied at 50-300 ppm inlet concentrations of H₂S. The increase in liquid flow rate, gas flow rate and inlet H₂S concentration increased the percentage removal of H₂S. The maximum of 78.88% removal of H₂S was observed at 27.65 × 10^-4 Nm³/s gas flow rate and 48.183 × 10^-6 m³/s liquid flow rate for 300 ppm inlet concentration of H₂S. A model has also been developed to predict the H₂S gas removal by using the results from the experiments and adding the parameters that affect the scrubber's performance. The deviations between experimental and predicted H₂S percentage removal values were observed as less than 16%.

Performance evaluation and optimization of field-scale bioscrubbers for intensive pig house exhaust air treatment in northern Germany

The treatment of exhaust air from three intensive pig houses in northern Germany by field-scale bioscrubbers (BS.1, BS.2, and BS.3) were evaluated monthly in 2015. The simultaneous removal of NH₃ and CH₄ was investigated by connecting a second bioscrubber (BS.2-2) to one of the three bioscrubbers (BS.2) to create a two-series connected bioscrubber (BS.2+BS.2-2). Additionally, whether isolated methanotrophic bacterial inoculation in BS.2-2 intensified CH₄ removal was examined. Average NH₃ removal efficiencies of 86%, 80%, and 77% were observed for BS.1, BS.2, and BS.3, respectively, under fluctuate NH₃ inlet concentrations (variation of 22%-54%) throughout the study year. However, average CH₄ removal efficiencies were lower than 10% in the three bioscrubbers. The pH of the recirculation water, which ranged from 5.7 to 8.1, was demonstrated to be an important factor for NH₃ removal and negatively correlated with NH₃ removal and NH₄⁺-N concentration in the recirculation water. The dominant NH₃-oxidizing and methanotrophic bacteria in the bioscrubbers, analysed by transmission electron microscopy, were Nitrosomonas sp. and Type I methanotrophs, respectively. NH₃ removal efficiency reached 100% in the two-series connected bioscrubber, however, CH₄ removal was still low (average of 2%). After inoculating isolated methanotrophic bacteria into BS.2-2, the average CH₄ removal was enhanced to 35%, offering a great option for bioscrubbers application to intensify CH₄ removal. Therefore, a two-series connected bioscrubber inoculated with methanotrophic bacteria would be an option for simultaneous removal of NH₃ and CH₄ from the exhaust air of animal houses.

Aerobic desulfurization of biogas by acidic biotrickling filtration in a randomly packed reactor

Biotrickling filters for biogas desulfurization still must prove their stability and robustness in the long run under extreme conditions. Long-term desulfurization of high loads of H2S under acidic pH was studied in a lab-scale aerobic biotrickling filter packed with metallic Pall rings. Reference operating conditions at steady-state corresponded to an empty bed residence time (EBRT) of 130s, H2S loading rate of 52gS-H2Sm(-3)h(-1) and pH 2.50-2.75. The EBRT reduction showed that the critical EBRT was 75s and the maximum EC 100gS-H2Sm(-3)h(-1). Stepwise increases of the inlet H2S concentration up to 10,000 ppmv lead to a maximum EC of 220gS-H2Sm(-3)h(-1). The H2S removal profile along the filter bed indicated that the first third of the filter bed was responsible for 70-80% of the total H2S removal. The oxidation rate of solid sulfur accumulated inside the bioreactor during periodical H2S starvation episodes was verified under acidic operating conditions. The performance under acidic pH was comparable to that under neutral pH in terms of H2S removal capacity. However, bioleaching of the metallic packing used as support and chemical precipitation of sulfide/sulfur salts occurred.