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Odour prevention in sewage treatment plants

2021-10-04 12:32:49

Odour prevention in wastewater treatment plants. Case: Cambrils WWTP

The Catalan Water Agency (ACA) commissioned a project to minimize the emission of odors from the primary sedimentation tanks of the Wastewater Treatment Plant (WWTP) of Cambrils (Tarragona), emissions that usually generated complaints from the neighborhood.

BION was selected as the candidate to carry out an interesting project that consisted in the treatment of gas phase pollutants (mainly H2S) emitted into the atmosphere.

The main source of odors in the primary settling tanks is the area where the clarified water falls to the next stage of treatment through small water jumps. It is at this point that significant amounts of volatile organic and inorganic compounds are released.

Bioconservacion suggested covering this area in order to prevent the release of free H2S into the atmosphere. Once this space was confined, two reactors were installed, packed with specific filter media for H2S elimination, namely BION Carb OX (with an adsorption capacity of up to 80% by weight).  Both reactors were designed to treat up to 750 m3 / h. 

 Implementation

A possible solution in this case is to confine the settler by installing a dome covering the entire tank and connecting the gas phase to media-packed reactors.  In this case, a 29 m diameter dome would be needed and the required processing capacity would be 20,000 m3/h. However, by confining only the problematic zone (outer crown) the flow to be treated would decrease to 1,500 m3/h. Obviously, this proposal also represents a much more economically advantageous civil work than a total confinement.

 In summary, the solution proposed by Bioconservacion represented a 50% saving in the initial investment compared to the usual solutions for this type of facility, and also a significant reduction in subsequent operating costs.

 In addition, the crown covers were designed in such a way that they could be removed from the perimeter of the sedimentation tank to facilitate maintenance tasks.

Removable cover along the perimeter of one of the primary sedimentation tanks

This installation was carried out at the end of June 2010, and since then, problems related to nuisance odor emissions have ceased.

Since its implementation, Bioconservacion has supplied the filter media and has maintained close contact with the plant's personnel. This collaboration allows us to better understand the real needs of each sector and to develop products that are better adapted to them. Among the projects that the Research and Development Department is working on, there is one that aims to carry out field tests with a new filter media developed specifically for environments with humidity above 99%.  Discussions are currently underway with the Cambrils WWTP to carry them out jointly at their facilities.

In our blog...

Treatment of Odors in Ventilation Ducts in Wastewater Tunnels

Odour treatment in sewage tunnel ventilation ducts Case Study: Izmir Wastewater Plant (Turkey) Project Description BION's distributor for municipal, biogas and odor treatment applications in Turkey, Biotek, has recently won a contract to supply equipment and filter media for odor abatement from ventilation ducts in wastewater tunnels in the municipality of Izmir, managed by IZSU. These tunnels are used to remove stale air in subway areas and replace it with fresh air, and are common in mines and wastewater plants. A wide variety of malodorous contaminants are present in these gases. Depending on the O2 content and the turnover rate, the compounds present can range from aldehydes, ketones or inorganic compounds such as NH3 or H2S, to the really problematic ones from anoxic processes such as dimethylsulfide, dimethyldisulfide, mercaptans, especially problematic because of low detection levels. The ventilation duct is 3.6 m in diameter. There are two aeration shafts in the tunnel, whose dimensions are 2.5x4 m and are closed with AISI 316L lids. The gas stream is passed through a tank packed with filter media in order to release contaminant-free air.   Odour problems generally appear between August and September.   Characterization of the gas stream  Biotek analyzed the composition of the vent effluent in order to find the most accurate solution in terms of filter media selection. The results revealed H2S concentrations and NH3 concentrations in the range of 1 to 5 ppmv, O2 content around 20% v v-1, while CO2 was measured at lower levels than in air. Interestingly, CH4 was measured at concentrations of about 0.5% v v-1, which may indicate a lack of O2 in certain areas of the duct.   Solution    After studying the composition and concentration of the odorous stream, as well as the design of the installation, Biotek with advice from BION, suggested the following proposal for tanks and filter media:   - BION ACPA in the bottom layer to remove NH3. - Mixture of BIONSIGMA and BIONISORB to remove H2S and low molecular weight volatile organic compounds.   It is important to note that the proposed solution has a higher capacity due to the presence of O2, which helps the BIONSIGMA to self-regenerate, prolonging the autonomy of the unit.   Descriptions of the filter media  BION ACPA is an adsorbent media impregnated with phosphoric acid. It has been widely used in applications involving odors and irritating gases associated with printers, fertilizers, cleaning products, urine and fish processing. BION ISORB is designed to successfully target a wide range of gases. It is especially recommended for the control of acid gases, nitrogen containing compounds, sulfur compounds and low molecular weight gases. BIONISORB uses a combination of two processes for contaminant removal. One of a physical nature, trapping the molecules inside the pellet due to its large internal surface area and a second by chemical oxidation. The oxidized gases are converted into harmless products. A particularity of BIONISORB is that it maintains its effectiveness even in the treatment of streams with relative humidity contents above 95%. This filter media is commonly used in applications such as wastewater treatment plants, pulp and paper plants, airports, chemical plants, refineries or laser cutting and engraving plants. BION SIGMA is a filter media especially suitable for H2S adsorption, consisting of an extruded pellet composed of a porous material and Fe(OH)3 iron hydroxide. Hydrogen sulfide is removed from the gas stream according to the following reaction:                                                2 Fe(OH)3 + 3 H2S ® 2 FeS + 1/8 S8 + 6 H2O   The generation of ferrous sulfide, FeS, changes the original color of the pellet from yellowish to blackish, indicating that the media has been consumed. Once exhausted, the media can be regenerated with air and the following reaction takes place:                                                2 FeS + 3/2 O2 + 3 H2O ® 2 Fe (OH)3 + 1/4 S8. No H2S is released during the regeneration process. Considering that one cycle is defined as the completion of these two reactions, BIONSIGMA can undergo at least 10 cycles before its total exhaustion, each cycle results in the removal of 45 mg H2S per gram of BIONSIGMA which means that the total removal capacity is approximately 450 mg H2S / g of filter media. In the absence of oxygen, BIONSIGMA shows a higher H2S adsorption capacity than a caustic impregnated activated carbon. On the other hand, the spent activated carbon cannot be regenerated and must therefore be discarded after a single cycle. The main application of BIONSIGMA is the removal of H2S in gas streams under anaerobic conditions, e.g. for biogas desulfurization. However, depending on the O2 content, BIONSIGMA can be used for the treatment of low H2S concentrations, as in this application, where the depletion and regeneration processes take place at the same time.  

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Odour treatment in WWTPs . SIMTEJO case (Portugal)

Controlling odor problems in sewage collectors and wastewater treatment plants is currently one of the main objectives to reduce and prevent potential problems related to worker safety and minimize the negative social perception that odor problems can generate.  The main sources of odor generation in WWTPs are the phases in anaerobic conditions, where the lack of oxygen favors the development of sulfate-reducing bacteria that use the sulfates present in the system and reduce them to H2S, in collectors and pumping stations.  BIOCONSERVACION recently signed a contract with SIMTEJO (Grupo Águas de Portugal) for the replacement of filter media in several pumping stations located in Lisbon (Portugal). The objective of the project was to reduce H2S levels below 1 ppmv. SIMTEJO is a reference company in Portugal whose main strategic objective is to control the pollution of water resources. Therefore, the collection and treatment of pollutants generated in domestic and industrial activities, the protection of water resources and the guarantee that water returns to nature free of pollutants are its main objectives. SIMTEJO aims to contribute to the well-being of about 1.5 million people in a geographical area of 1000 km2.  Pumping station characteristics  All the pumping stations present a spectrum of pollutants very similar in type and concentration, which are notably increased during the summer season. - The pumping stations are installed outdoors, with the exception of some that are underground due to their sensitive urban location. - The purification systems that have been implemented are basically standard upflow reactors. However, in some pumping stations, where higher flows are treated, Split type reactors have been installed in order to achieve better performance. Characterization of emissions in pumping stations   Emissions generated in pumping stations normally contain a large number of volatile organic compounds (VOCs), H2S concentrations in the range of 10-30 ppmv, as well as other pollutants such as NH3 or mercaptans among others, depending on the nature of the wastewater. Occasionally, H2S concentration peaks of up to 100-200 ppmv can be measured. The objective is to reduce H2S concentration levels below 1 ppmv, as well as the rest of the malodorous contaminants.   Solution Considering the nature of the emissions we are dealing with, BION carb OX was chosen as the most suitable media for the case, due to a number of advantages: - BION Carb OX consists of a combination of very high quality wood activated carbon and a unique blend of inorganic catalytic phases, which enables an extraordinarily high H2S adsorption capacity to be achieved (80 kg H2S/100 kg BION Carb OX). - Unlike other products, BION Carb OX does not convert H2S to sulfuric acid (H2SO4), which could lead to corrosion problems in equipment and make it difficult to dispose of the waste generated. - Instead, the active centers of the metal oxides in BION Carb OX catalytically convert H2S to sulfur (S). The sulfur then migrates and accumulates in the micropores of the activated carbon. Consequently, the metal oxides are again available to oxidize new H2S molecules. - BION Carb OX also performs very well in the removal of other acid gases such as sulfur dioxide (SO2) or hydrogen chloride (HCl). In addition, it is a remarkably effective means of removing some VOCs that may be present in the gas stream to be treated. - Unlike in the case of impregnated coals, the presence of high concentrations of CO2 does not affect the H2S absorption capacity. - Minimization of the risk of fire, due to the very high ignition temperature of the product (420 ºC).  In summary, BION Carb OX is an ideal product for use in wastewater treatment plants due to its high H2S adsorption capacity, as well as its good performance with other malodorous compounds such as methyl mercaptan and some VOCs. Other applications include refineries, paper industry, pumping stations and sludge tanks.  In-service media evaluation   BION continues to work with the end customer after the solution has been implemented and verifies the result. By evaluating the remaining capacity of the media it is possible to re-optimize the process in order to obtain the maximum profitability of the installation.   Moreover, BION tracks the evolution of several key operating parameters by means of versatile sensors that can be easily placed in the reactors. With the data collected, BION is able to re-adapt and re-optimize the process on a facility-specific basis. This strengthens the customer-supplier relationship, which results in technical improvements to the facility itself.

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Deodorization project: ROPEC WWTP (Ottawa)

Project Description BION has recently been awarded the supply of high capacity odour removal filter media for two deodorization systems at a wastewater treatment plant (WWTP) located in the Canadian capital, Ottawa. The Robert O. Pickard Environmental Centre (ROPEC) is located in the east end of the city, right next to the Ottawa River. Using an extensive sewer network, it collects all wastewater from urban and industrial areas between Stittsville, Orleans and Manotick. The ROPEC WWTP treats an average of 390 million liters of wastewater per day, generating 39 tons of dry biosolids per day, which are used as agricultural fertilizer. The ROPEC treatment plant has a significant number of carbon-packed tanks to purify all the polluted streams generated in different areas of the plant. They are all vertical fixed beds, packed with filtering granules supported on fiber-reinforced plastic grids (Figure 1). The media tanks were originally designed for in situ regeneration (using water and caustic solutions). However, regeneration is an arduous process and the filter media tended to lose, on average, 70% of its initial capacity. In order to obtain an optimal solution, the City of Ottawa launched a tender for the supply of activated carbon, determining a number of criteria (capacity, odor removal efficiency, surface area, pore size distribution, bulk density, etc...). After evaluating all the bidders, Chemco Inc, Bioconservacion's Canadian distributor, was awarded the contract to supply the replacement filter granules for the deodorization of the Pretreatment zone (grids) and Biosolids.   Characterization of Wastewater Treatment Plant Emissions   Typical gaseous emissions at a WWTP include a large number of volatile organic compounds (VOCs), H2S at concentrations between 10 - 50 ppmv, reduced sulfur compounds and other pollutants such as NH3 or mercaptans among others. Depending on the nature of the wastewater and the area of the plant, the concentration of the contaminants can vary in composition and concentration.   The objective of this project was to reduce H2S concentration levels to concentrations below 1 ppmv, as well as decreasing concentrations of the other odorous pollutants.   The ROPEC WWTP deodorization tanks can be divided into three main areas, where the composition of the streams is assumed to be similar. This consideration was carried out assuming a relative humidity of at least 90% and a temperature between 10 - 30 ° C. The areas considered and the requirements of the granulates without the following: Pretreatment Zones: require granulates with high capacity for the removal of H2S, reduced sulfur compounds (mainly DMS, DMDS, MM) and a wide variety of volatile organic compounds (VOCs). Biosolids Zone: requires granulates with high affinity for H2S, reduced sulfur compounds (mainly DMS, DMDS, MM), volatile organic compounds (VOCs) and ammonia / amines. Solution   After studying the composition and concentration of the flows to be treated, as well as the design of existing facilities, Bioconservacion proposes the following solution: - Pretreatment zones: 100% BION Carb OX. - Biosolids Zone: 75% BION Carb OX and 25% BION ACPA. It is important to note that the proposed solution does not require any regeneration, which simplifies the operation of the purification systems.   Description of the filtering granulates: BION ACPA consists of a carbon impregnated with an acidic compound for the reduction of basic contaminants, such as ammonia or amines. BION carb OX consists of a high quality wood activated carbon and a unique blend of inorganic catalytic phases, which allows an extraordinarily high H2S adsorption capacity up to values of 80% w/w (80 kg H2S/half kg 100). Compared to other products, BION carb Ox does not convert H2S into sulfuric acid (H2SO4), which could cause corrosion problems in equipment. The active metal oxide centers of BION Carb OX convert H2S into sulfur (S). This sulfur subsequently migrates and accumulates in the micropores of the activated carbon. As a result, the metal oxides are again available to oxidize new H2S molecules.   BION carb OX achieves very effective results in the removal of other acid gases such as sulfur dioxide (SO2) and hydrogen chloride (HCl). In addition, it is a very effective granulate for the removal of volatile organic compounds, which are most likely to be found in the gas stream to be treated.   Unlike other impregnated carbons, the high H2S adsorption capacity is not affected, even in the presence of high CO2 levels. In addition, it has a high ignition temperature (420 ºC), which minimizes the risk of bed fire.   Thanks to these advantages, BION carb OX filter granules are ideal for use in wastewater treatment plants due to their high H2S removal efficiency, as well as their affinity for other typical malodorous compounds such as mercaptans and a wide range of volatile organic compounds. Other applications where this granulate can be used are: refineries, pulp and paper mills, pumping stations, sludge storage tanks, composting facilities, etc.   Performance evaluation   BION offers a customized service through a close relationship with our partners and end customers, which continues once the solution has been implemented. Chemco and Bioconservacion visit this plant once the contract has been awarded, before the supply of the filter granulates and during the changeover, in order to witness the installation and answer any questions that may arise.   BION also offers the service of performing a remaining life analysis of the filtering granulates, halfway through their estimated life, in order to optimize the replacement of the granulate mix, in the event that the actual working conditions differ from the initial ones taken into account in the characterization.  

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