Effectiveness of Biotrickling Filters as Standalone Technology to Treat Municipal Odors in Harsh Desert Environments - Case Study

Treatment of odors from municipal sewage collection systems and wastewater treatment plants often proves challenging in harsh middle east climate conditions. Some of the main challenges include underestimation of the odor concentrations in the municipal collection systems and wastewater treatment plants, and the selection of inappropriate odor treatment technologies for these applications. Odor concentrations are often orders of magnitudes higher than what is experienced in the USA and other Western climates, which is mostly attributed to the very high summer ambient temperatures and often long residence times of the sewage in the collection systems. This paper provides an overview of a comprehensive odor study that was performed at the headworks of the Al Filaya WWTP in Ras Al Khaimah (WWTP), UAE to determine the design criteria for the odor control system. It also reports on the successful implementation of biotrickling filter technology to treat the odors at the headworks. In 2021 Ras Al Khaimah Wastewater Agency (RAKWA) contracted with BioAir Solutions to perform a comprehensive odor study at the newly constructed headworks at the WWTP to determine suitable design criteria for the odor control system. The study included the measurement of both liquid phase pH, temperature, and dissolved sulfide, as well as vapor phase H2S, methyl mercaptan, ammonia and ammine concentrations. It also included the estimation of suitable air ventilations rates from the various odor sources at the headworks, including the inlet chamber, screen channels, vortex grit removal system and others. The odor study revealed that the sewage at the headworks is very septic, and the dissolved sulfide concentrations vary between 12 mg/L and 32 mg/L. Henry's law equilibrium calculations, which incorporated sewage pH, dissolved sulfide, and temperature, resulted in an equilibrium vapor phase H2S concentration of between 580 and 3,200 ppmv. The final design basis for the odor control system was 3,500 Am3/hr of airflow at design average and peak H2S concentrations of 2,350 ppmv and 3,525 ppmv, respectively. The required H2S concentration in the air after treatment was < 0.25 ppmv, which equites to 99.99% H2S removal efficiency. Biotrickling filter technology was selected as the most suitable technology for the application. RAKWA decided to upgrade the existing biotrickling filter and add a second reactor to treat the odors at the headworks. BioAir Solutions supplied and installed two EcoFilter biotrickling filters which were put in operation in December 2021 (see Figure 1). Once the system was fully acclimated, its performance was tested to validate that it achieved < 0.25 ppmv H2S concentration in the discharge stacks of the two reactors. Figure 2 provides the performance data for the two EcoFilter reactors. This case study demonstrates the importance of performing odor studies to verify the odor concentrations and ventilation rates for existing WWTP applications in harsh climate environments. If new greenfield WWTPs are developed, it is important to use data from similar other plants in the region to develop a suitable design basis for the odor control system. The study further demonstrates the suitability of biotrickling filter technology for successful odor removal in hot middle east environments, without the need for secondary carbon polishing. It is, however, very important that the system be design for the appropriate H2S concentrations to avoid media failures that may occur if the actual H2S concentration is much higher than the design H2S concentration.