Environmental Engineering Podcast - Shane Gillespie

The episode discusses wastewater treatment systems in Ireland, focusing on biological treatments to meet EU environmental standards. The activated sludge process is highlighted, involving an aeration tank and clarifier to remove organic matter. The Muntin Island Wastewater Treatment Plant in Galway is a common facility. Challenges include energy-intensive processes, excess sludge production, and meeting new regulations. Understanding volumetric loading rates is crucial for efficient operation. The need for more sustainable practices is emphasized due to increasing sludge waste volumes and disposal challenges. Hello and welcome to Environmental Engineering Question Time. My name is Shane and today I am joined by final year student Ciara. Welcome Ciara. Today we will explore wastewater treatment systems with a focus on biological treatments. Did you know that a report from the EPA 2024 estimated that over 1 billion litres of wastewater are generated in Ireland every day? Wastewater contains organic material, nutrients and pathogens which can cause oxygen depletion and neutrification in water bodies. EU legislation such as the Water Framework Directive and the Wastewater Treatment Directive establish standards to ensure environmental protection. To comply, wastewater must pass through a series of intensive treatment stages. Now I will hand over to you Ciara for your first question. Thank you Shane. I would like to know what happens after each stage of treatment. Wastewater first undergoes screening and primary treatment to remove large solids and saturated material. It is then directed towards secondary or biological treatment. This is where the dissolved organic matter is removed using the activated sludge process. In some cases, waste then receives a tertiary treatment. What actually is the activated sludge process? How does it work? This process consists of two main components, an aeration tank and a secondary clarifier. Have a look at an article titled The Evolution of Activated Sludge Process. It is especially useful for explaining this. First, wastewater enters the aeration tank, where it is mixed with a biomass substrate. Treatment occurs through absorption, where organic matter attaches to suspended microbial clusters, forming activated sludge. As oxygen is released into the tank, oxidation occurs, with biomass breaking down the organic material into carbon dioxide, water, ammonia and new biomass. After aeration, a mixture flows into the clarifier. Here the sludge settles out, producing a clarified effluent layer at the top. Sludge is wasted from the bottom and effluent is removed to be discharged back into the environment. Ore is then for further treatment. A crucial aspect of this process is sludge recycling, where a portion of the settled sludge is returned to the aeration tank to maintain a high concentration of biomass. Do you have the treatment facility in Ireland? Yes, it is actually the most common type of biological treatment in Ireland. A good example to look at is the Muntin Island Wastewater Treatment Plant, located just off the coast of Galway. It recently underwent a series of upgrades to improve treatment capacity. How would a treatment plant know how much pollutants it has to treat? That is the volumetric load, and that is the common design parameter that is based on knowing how much pollutants is coming into the plant. For a Muntin Island with a maximum capacity of approximately 170,000 population equivalent, you would need to consider the system running at full capacity. The EPA Code of Practice report tells us that an average BOD load is 60 grams per person per day, so then our daily load would be our population equivalent times average BOD load, and that would give us 10,200 kg per day. If we were to assume that we had 10 aeration tanks on site, each with a volume of 500 m3, the total volume would be 5,000 m3. To calculate the volumetric loading rate is 10,200 divided by 5,000 to get 2.034 kg of BOD per m3 per day. This is especially important to know when operating biological treatment, so that hydraulic retention time and food-to-microorganism ratios can be calculated. What are the advantages and disadvantages of biometric treatment? The main benefit is the production of a high-quality effluent, particularly in terms of BOD and nitrogen removal. However, it comes at a cost. The activated sludge process is very energy-intensive, mainly due to aeration, and also the large volumes of excess sludge that are produced, which need to be landfilled. This has actually become a big problem in wastewater treatment, because of the recast urban wastewater treatment directive, which states that wastewater treatment plants must become more efficient and sustainable. What is the main challenge of the Milton Island wastewater treatment plant to comply with the new regulations? The plant may be able to offset energy usages by transitioning to more energy-efficient technology or creating energy on-site, but the larger concern that I see for this plant are the large volumes of sludge wasted from the treatment. Ishka Arun's National Sludge Management Plant estimated that in Galway City in 2020, there were 2,294 tonnes of sludge wasted, and that that would likely rise to 3,332 tonnes by 2040. Galway City Council also raised concerns over sludge disposal, which is becoming increasingly challenging to manage due to new regulations. I hope I've shown that there are a lot of complexities to this system, but I'm afraid we've run out of time for today. Ciara, thank you very much for coming on, and for all your insightful questions. I hope that this brief introduction to the topic has opened your mind to the complex challenges that lie ahead in our wastewater treatment system. Yes, it has. It's been really interesting. Thank you so much. Thank you for tuning in, and I hope to see you all on the next episode. Goodbye.