In-pipe microbial fuel cell system for hydrogen sulfide control in wastewater collection networks

Abstract

The invention provides an integrated in-pipe microbial fuel cell system designed to control hydrogen sulfide within wastewater collection networks. The system utilizes an anode positioned in the anaerobic sediment layer and a cathode in the oxygen-rich upper wastewater zone. As hydrogen sulfide is electrochemically oxidized at the anode, electrons are released and transferred to the cathode, where they reduce oxygen and generate electrical energy. This process reduces hydrogen sulfide levels, preventing corrosion and odor formation, while simultaneously producing power for monitoring devices. The system offers a sustainable, low-maintenance solution without the need for continuous chemical dosing.

Description

[0001] In-Pipe Microbial Fuel Cell System for Hydrogen Sulfide Control in Wastewater Collection Networks

[0002] Field of the Invention

[0003] The present invention pertains to the field of urban wastewater management and focuses on solving one of the most challenging issues in wastewater collection systems: the generation and accumulation of hydrogen sulfide (H2S). This compound is responsible for severe corrosion of concrete and metal infrastructure, unpleasant odors, and potential health hazards (1). Traditional control strategies rely on chemical dosing or mechanical aeration, which are costly, energy-intensive, and difficult to maintain across vast sewer networks (2). The invention introduces an innovative approach by integrating a microbial fuel cell (MFC) directly within the wastewater pipe. This unique configuration harnesses the natural biochemical activity occurring in the sewer environment to electrochemically oxidize hydrogen sulfide at its point of generation, preventing both odor and corrosion. By strategically placing the anode in the anaerobic sediment layer and the cathode in the oxygen-rich upper wastewater zone, the system exploits natural redox gradients within the pipe.

[0004] As hydrogen sulfide is biologically or electrochemically oxidized at the anode, electrons are released and captured through an external circuit (3). These electrons are then transferred to the cathode, where they react with oxygen to form water, completing the circuit and producing usable electrical energy (4). This process transforms hydrogen sulfide — a destructive waste product — into a source of renewable energy. The integration of this technology into sewer systems provides a sustainable, self-powered, and maintenance-friendly solution for hydrogen sulfide management. Unlike conventional chemical treatments, this system requires no continuous external chemical inputs, making it economically efficient and environmentally friendly. Furthermore, the electricity generated can be used to power sensors, monitoring devices, or other low-energy equipment within the sewer network. This invention represents a significant advancement in wastewater treatment by combining real-time pollutant removal, infrastructure protection, and energy recovery into a single, compact, and scalable system. Background of the Invention

[0005] The generation of H2S in wastewater collection networks represents a pervasive and economically burdensome challenge for municipal infrastructure systems globally (5). This problematic compound originates from complex biochemical pathways mediated by specialized anaerobic microorganisms. Sulfatereducing bacteria (SRBs), primarily of the genera Desulfovibrio and Desulfobacter, thrive in the anaerobic sediments accumulated at the invert of sewer pipes (6, 7). These facultative anaerobes utilize sulfate (S042-), which is abundant in wastewater, as a terminal electron acceptor during the oxidation of organic matter (simplified as CH2O) or hydrogen (8). The core metabolic pathway can be summarized by the following stoichiometry:

[0006] S042’ + 2C(organic) + 2H2O H2S + 2HCO3’ + OH“

[0007] This dissimilatory sulfate reduction process generates hydrogen sulfide, which subsequently partitions into the aqueous phase. A critical equilibrium determines its form:

[0008] H2S(aq) HS" + H+(pKa « 7.0) S2’ + 2H+

[0009] In the typical slightly acidic to neutral pH environment of sewage, a significant portion exists as gaseous H2S. This volatile compound can escape into the pipe headspace, presenting a dual menace. First, its release into the atmosphere creates a profound public nuisance due to its extremely low odor threshold (~0.5 ppb) and characteristic rotten-egg smell, alongside potential health impacts at higher concentrations. Second, and more critically, within the moist, oxygen-rich environment of the pipe crown, chemoautotrophic bacteria, namely Acidithiobacillus spp., oxidize H2S to sulfuric acid (H2SO4):

[0010] H2S + 2O2H2S04

[0011] This biogenic sulfuric acid directly attacks the concrete matrix, dissolving the calcium hydroxide and calcium silicate hydrate compounds that provide structural integrity, leading to severe microbial-induced corrosion (MIC) (9, 10). This process drastically shortens the asset's lifespan from decades to a mere 10-15 years, necessitating extraordinarily costly repairs and rehabilitation.

[0012] Conventional mitigation strategies are predominantly reactive and resourceintensive. Chemical dosing, involving the continuous addition of oxidants like nitrate (NO3“), iron salts (e.g., FeCI3), or hydrogen peroxide (H2O2), aims to either suppress SRB activity or oxidize H2S after its formation (11). For example, nitrate addition promotes the growth of sulfate-reducing nitrate-reducing bacteria (SRNRBs) that outcompete SRBs, while ferric chloride precipitates sulfide as ferrous sulfide (FeS). Alternatively, extensive air treatment systems, such as chemical scrubbers or biofilters, treat the foul air extracted from sewer headspaces. These approaches are financially burdensome due to ongoing chemical and energy costs, operationally complex to manage, and often merely transfer the problem — either downstream by converting sulfide to other compounds or to the air phase — rather than solving it at its source.

[0013] While MFC technology has been demonstrated for organic load removal in controlled reactor settings, typically at wastewater treatment plants, its application has not been effectively extended to a practical, in-pipe system (12-14). These prior applications primarily leverage the oxidation of organic carbon by exoelectrogenic bacteria (e.g., Geobacter spp.) for electron production. The key innovation gap lies in the development of a system specifically designed to harness the distinct chemistry of hydrogen sulfide oxidation — a substrate with a higher energy potential than organics — by sulfur-oxidizing bacteria (e.g., Thiobacillus or Acidiphilium spp.) or direct electrochemical oxidation. A practical implementation for combined in-situ corrosion abatement and energy recovery within the hydraulically and chemically dynamic confines of a live sewer environment remains an unmet challenge, which the present invention addresses. The electrochemical oxidation of H2S can be described through a well-known reaction pathway. When H2S is completely oxidized to sulfate, the anodic half-reaction proceeds as follows (15):

[0014] H2S + 4W2O SOl~ + 10W+ + 8e~ This reaction shows that eight electrons are released for each mole of H2S fully oxidized to sulfate. This 8-electron pathway is widely documented in studies of electrochemical and biological sulfide oxidation and is a key basis for designing systems that convert sulfide into electrical energy. Using Faraday’s law, the total theoretical charge Q that can be produced from this oxidation can be calculated. The relationship is given by:

[0015] Q = n x F x Nmolwhere n is the number of electrons per mole (here, 8), F is the Faraday constant (96485 C mol-1), and Nmoi is the number of moles of H2S oxidized. The number of moles is found by dividing the mass of H2S (mH2S) by its molecular weight (MH2S), which is 34.08 g mol-1. Substituting into the equation gives:

[0016] For a mass of 1 mg of H2S (0.001 g), the theoretical charge is:

[0017] 0.001

[0018] Qima = 8 X 96485 X34 08« 22.65C

[0019] This means that, under ideal conditions, 22.65 coulombs of charge can be generated for every milligram of H2S completely oxidized to sulfate (15). This value provides a maximum theoretical limit that can be used for the initial design of sulfide- driven fuel cells or microbial fuel cells. The charge can also be expressed in ampere- hours (Ah), since 1 Ah = 3600 C. Converting the charge gives:

[0020] Qimg=0.006294 / r = 6.29mAh

[0021] To estimate the total energy output, the actual working cell voltage and coulombic efficiency must be considered. The energy in joules (Ej) and watt-hours (Ew) can be calculated as:

[0022] Ej = Q X ECellX T|c Here, Eceii is the operating voltage of the fuel cell, and qc is the coulombic efficiency, which represents the percentage of electrons that are successfully captured as useful current. For example, if the cell voltage is 0.6 V and the coulombic efficiency is 50% (0.5), the energy produced per milligram of H2S would be approximately:

[0023] Energy in joules:

[0024] Ej = 22.65 X 0.6 X 0.5 = 6.8 /

[0025] Energy in watt-hours:

[0026] 6.8

[0027] These calculations give a direct way to estimate the potential energy yield of a sulfide-driven fuel cell, which can be essential for the design and optimization of systems aimed at both energy recovery and waste treatment, the complete oxidation of hydrogen sulfide to sulfate releases a significant number of electrons, making it a highly effective fuel for electricity generation in microbial fuel cells. By applying Faraday’s law, the theoretical energy that can be recovered from a given mass of H2S can be accurately estimated. This demonstrates the strong potential of sulfide-driven fuel cells for both energy recovery and pollution control. In wastewater collection networks, this approach not only helps to mitigate odors and corrosion caused by H2S but also provides a sustainable source of renewable energy. Therefore, an in-pipe microbial fuel cell offers a compact and efficient solution for real-time H2S removal while generating electricity directly at the point of treatment. This dual benefit positions the technology as a valuable innovation for modern wastewater management systems.

[0028] Summary of the Invention

[0029] The invention provides a system and method for the in-situ control of hydrogen sulfide and the generation of electricity within a wastewater collection pipe by exploiting its inherent electrochemical potential. The core of the invention is a microbial fuel cell apparatus comprising an anode strategically installed within the anaerobic sediment layer at the pipe invert and a cathode suspended within the oxygenated wastewater flow. This configuration capitalizes on the natural chemical gradient present in the pipe. At the anode, electroactive microbes catalyze the oxidation of hydrogen sulfide, producing elemental sulfur, protons, and electrons. This process effectively removes the dissolved sulfide, eliminating the primary cause of odour and corrosion. The liberated electrons are then conveyed through an external circuit to the cathode, where they combine with protons and oxygen to form water, thereby creating a continuous electrical current. The system operates autonomously, requires no chemical additives, and transforms a destructive waste product into a valuable source of renewable energy, offering a sustainable and scalable solution for municipal wastewater infrastructure.

[0030] Description

[0031] Detailed Explanation of the System and its Components

[0032] The system operates by utilizing the fundamental principles of a microbial fuel cell, adapted to the unique environment of a sewer pipe. The key innovation lies in the strategic placement of the electrodes to leverage the natural chemical and biological gradients present. The anode (4) is a crucial component and serves as the site for the oxidation of hydrogen sulfide. It is constructed from a conductive, non- corrosive, and biocompatible material such as carbon felt, graphite rod, graphite fiber brush, or stainless steel, which provides a high surface area for microbial colonization. It is installed directly within the sediment layer (3) at the pipe's invert, ensuring it is positioned within the anaerobic zone where sulfate-reducing bacteria are active and hydrogen sulfide is present. The cathode (5) serves as the site for the reduction of oxygen. It is also constructed from a conductive material, typically coated with a catalyst such as platinum or activated carbon to enhance the oxygen reduction reaction. Its position in the oxygen-rich zone of the wastewater flow, near the surface, is critical for ensuring a sufficient supply of the terminal electron acceptor (oxygen) to sustain the electrochemical reaction. The external electrical circuit (6) completes the system, allowing for the flow of electrons from the anode to the cathode. This circuit is the conduit for the electrical energy generated. It can be connected to a maximum power point tracker (MPPT) to optimize energy harvesting and to storage devices or low-power applications like wireless sensors for monitoring pipe conditions, creating a self-powered monitoring system. Detailed Explanation of the Method and Operation

[0033] A fuel cell is a device that changes chemical energy into electrical energy through a chemical reaction. This process keeps working as long as fuel and oxygen are supplied. Recent research has explored the use of hydrogen sulfide (H2S) as a novel fuel source. Traditional fuel cells typically use hydrogen or hydrocarbons; however, hydrogen sulfide may be a viable alternative because it is common and possesses unique chemical properties. Scientists are studying how to make fuel cells using hydrogen sulfide work better and more practically. This could help produce clean energy and manage waste at the same time (12-14). A microbial fuel cell (MFC) is a device that makes electricity from chemical energy using microorganisms. In an MFC, microbes break down substances like hydrogen sulfide (H2S) to produce electrical power. In the anode part of the cell, hydrogen sulfide can be changed into elemental sulfur.

[0034] This process helps clean waste while also creating electricity. For example, breaking down hydrogen sulfide in an MFC can produce about 101 milliwatts of electrical power. This ability to treat waste and make electricity shows that MFCs could be useful for clean energy and waste management (16). An up-flow anaerobic sludge blanket (LIASB) reactor has been modified into an MFC to test its ability to treat waste and produce energy. Experiments showed good results: the MFC removed 98% of acetate and lowered sulfate levels by 46%. This shows the MFC works well for breaking down organic waste and controlling sulfate. Using this system to remove hydrogen sulfide from wastewater is especially interesting. Figure 1 shows this idea and how an MFC can be used in wastewater treatment (17). Besides removing hydrogen sulfide, MFCs can also produce electricity. They work like this: MFCs use bacteria to turn chemical energy into electrical energy through electrochemical reactions. In wastewater treatment pipes, hydrogen sulfide is handled by an MFC system in the following way: (a) In wastewater pipes, oxygen is very low beyond 0.4 mm depth. In these conditions, sulfate-reducing bacteria use sulfate (S042-) and organic carbon to produce carbon dioxide and hydrogen sulfide, (b) When hydrogen sulfide reaches the MFC anode, it is oxidized. This changes hydrogen sulfide into elemental sulfur, protons (H+), and two electrons (see Figure 1).

[0035] Anode Reaction: H2S — > S° + 2H++ 2e Elemental sulfur does not dissolve, which helps stop more activity of sulfatereducing bacteria, (c) The electrons from this reaction travel through an external circuit to the cathode. There, they meet protons and oxygen to form water.

[0036] Cathode Reaction: O2+ 4H++ 4e~ — > 2H2O

[0037] This electron flow produces electricity, (d) By turning hydrogen sulfide into elemental sulfur and producing electricity, the MFC also reduces odor and prevents corrosion in wastewater systems. Even though a single microbial fuel cell produces only a small amount of electricity, placing many cells along long wastewater pipes could generate a substantial total power. This idea is still theoretical, and no real- world studies have tested it in wastewater pipelines yet. However, it shows potential for combining waste treatment with energy production (17-22). Figure 1 shows a cross-section of a wastewater collection pipe. Two electrodes are installed inside the pipe. One electrode is placed at the bottom, within the sediment, and the other is near the water surface in the middle of the pipe. Over time, sediment builds up at the pipe bottom, increasing microbial activity in that area. As a result, aerobic processes in the sediments gradually stop, and anaerobic processes dominate. In this condition, the electrode near the water surface (aerobic zone) acts as the cathode, while the electrode at the pipe bottom (anaerobic zone) acts as the anode. Microbial activity around the electrodes generates a potential difference between them, which helps prevent hydrogen sulfide formation in the anaerobic zone. If such electrodes are installed throughout a wastewater collection network, which can span hundreds of kilometers, the system can prevent odor and corrosion in the pipes while also producing electricity.

[0038] Advantages and Scalability

[0039] The system provides a direct and elegant solution to the problem of hydrogen sulfide by intervening at the precise point of generation. It transforms a damaging waste product into electricity, offsetting its own cost and potentially powering ancillary equipment. A single unit may generate a modest amount of power (e.g., 50-150 milliwatts), but the modular nature of the invention allows for the deployment of hundreds or thousands of units across a extensive network spanning hundreds of kilometers. The cumulative effect would be a significant reduction in hydrogen sulfide concentration network-wide, leading to extended infrastructure lifespan and the generation of a substantial amount of decentralised renewable energy. This scalable, distributed approach to wastewater management is a key advantage of the present invention.

[0040] A primary object of the invention is to provide a system for controlling hydrogen sulfide in wastewater pipes that operates without chemical consumption, thereby offering a more sustainable and cost-effective alternative to prior art systems. A further object is to provide a system that not only abates hydrogen sulfide to prevent corrosion and odour but also generates useful electrical energy from the oxidation process, creating potential operational cost savings. Another object is to provide a method for mitigating infrastructure degradation in wastewater networks that is simple to implement and leverages the existing conditions within the pipe. Yet another object is to provide a modular and scalable system whose components can be deployed throughout extensive networks of wastewater pipelines to provide collective and significant benefits.

[0041] The present invention will now be described in detail with reference to the accompanying drawing, which illustrates a preferred embodiment by way of nonlimiting example.

[0042] Figure 1 provides a schematic cross-sectional view of a wastewater collection pipe (1) equipped with the MFC system. The pipe (1) contains flowing wastewater (2) and has a layer of sediment (3) accumulated at its bottom, a common occurrence in such networks. The system comprises two primary electrodes: an anode (4) and a cathode (5). The anode (4) is embedded within the anaerobic sediment layer (3) where hydrogen sulfide is generated. The cathode (5) is suspended within the bulk wastewater (2), preferably near the air-liquid interface where oxygen concentration is highest. The two electrodes are connected by an external electrical circuit (6), which includes wires and may also contain a device for storing or utilizing the generated electrical energy, such as a capacitor, battery, or sensor. Brief Description of Drawings

[0043] [Fig 1]: Schematically figure of wastewater collection pipes protection against hydrogen sulfide by using microbial full-cell.

[0044] The figure shows a schematic cross-section of the in-pipe microbial fuel cell system illustrating the placement of the anode within the sediment layer and the cathode within the wastewater flow.

[0045] References:

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Claims

1. Claims1. An in-pipe microbial fuel cell system for controlling hydrogen sulfide in wastewater collection networks, comprising: (a) a wastewater pipe; (b) an anode positioned within an anaerobic sediment layer of the wastewater pipe; (c) a cathode positioned in the oxygenated upper region of the wastewater flow; (d) an external electrical circuit connecting the anode and cathode; (e) wherein hydrogen sulfide is electrochemically oxidized at the anode, releasing electrons that are transferred through the circuit to the cathode, thereby reducing oxygen and generating electrical energy while simultaneously reducing hydrogen sulfide concentration in the wastewater.

2. The system of claim 1 , wherein the anode is made of a carbon-based material, iron, or aluminum selected from graphite, carbon cloth, or carbon felt.

3. The system of claim 1 , wherein the cathode includes a catalyst to enhance oxygen reduction reactions.

4. The system of claim 1 , wherein the generated electricity is used to power sensors or monitoring devices within the sewer network.

5. The system of claim 1 , wherein the anode and cathode are modular and replaceable without disrupting wastewater flow.

6. The system of claim 1 , further comprising a control unit to monitor current flow and hydrogen sulfide concentration in real time.

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