Aijie Wang

With a great deal still to do to meet the water supply and sanitation aims of the UN Sustainable Development Goals, there is a practical need for solutions that can be applied at scale and at speed. These aims do feature prominently in the global conversation on water, not least in the UN Water Action Agenda. The question is how to advance the options that respond to the practical need for solutions. The water sector can learn lessons from other sectors about how to unlock the opportunities for game-changing innovations – innovations in which anaerobic digestion technologies have an important part to play. Here, decentralised approaches are key as they allow action at speed, they provide flexibility to adjust as options evolve, and they contribute to resilience. Not only can decentralised approaches contribute in these ways to meeting sanitation needs, they can disrupt the status quo that is focused on centralised approaches, building on successful application to contribute increasingly comprehensive, market-driven coverage.

Implementing innovative biotechnologies to recover value-added products with simultaneous waste treatment can provide alternatives to fossil-fuel based products, address environmental problems, and strengthen the bioeconomy. This talk will highlight top-down and bottom-up approaches to harness microbiomes for treating and converting waste streams such as food and brewery waste and lignocellulosic biomass into valuable resources. Chain elongation is one such emerging biotechnology that employs a top- down approach through an ecological selection of anaerobic microbiomes to produce platform chemicals called medium chain carboxylic acids from diverse waste streams. The bottom-up approach will be discussed to systematically study environmental isolates that are potential biocatalysts for lignocellulosic (agricultural) biomass conversion. Integrating top-down and bottom-up approaches for microbiome engineering will ultimately enable us to leverage the diverse metabolic capacity of microorganisms for diverse environmental and biotechnology applications.

The transition from traditional wastewater and waste treatment plants to more advanced processes that enable the efficient recovery of resources has become a scientific, technological, economic, and social challenge. In this regard, anaerobic digestion plays a crucial role as it not only helps reduce greenhouse gas emissions but also paves the way for new industrial development models.

The “Carboxylate platform” is based on transforming biowastes (hundreds of different molecules) by anaerobic fermentation into a few numbers of volatile fatty acids (VFA), including Lactic acid, which are essential to produce useful chemicals. This presentation will delve into the importance of thermodynamic, kinetic, and stoichiometric principles in guiding anaerobic fermentation towards selective production of VFAs. Our research group has developed a metabolic model simulating the anaerobic fermentation process and predicting the VFA production yields under different conditions. The model has undergone a rigorous validation process, using experimental data, and has consistently shown promising results in predicting the optimal conditions for enhancing the selective production of the desired VFA. Furthermore, we will discuss the current state of the art and several pilot or industrial-scale projects that aim to produce VFAs,

Polyhydroxyalkanoates (PHA), and Medium Chain Fatty Acids (MCFA) from a variety of feedstocks, such as agricultural waste, industrial effluents, and municipal solid waste. Finally, the opportunities of the platform based on lactic acid will be analysed.

Anaerobic digestion of sludge and slurries from wastewater treatment plants has been a core topic in AD conferences for many decades. While sludge stabilization was a primary driver, the concomitant energy recovery positioned anaerobic digestion centrally in greening conventional activated sludge (CAS) systems. What is the status of sludge digestion and what are the current developments in application and fundamental research? What limits the bioconversion and what techniques can be applied to maximize this. Thermal hydrolysis processes (THP) are increasingly applied to maximize biogas production, but THP also impacts AD functionalities, sometimes resulting in less biogas than expected. Can we predict the effects? Do we need alternatives for THP? With enhanced sludge digestion, also the reject waters get more concentrated. While anammox is being implemented to reduce the N load, increasing concerns for non-controlled N₂O emissions and potential cultivation of Legionella at the treatment sites call for alternative approaches. Step away from biology and embracing physicochemical techniques? Recent research has shown that we can also recover the biochemical energy enclosed in ammonia. May this help in further greening the CAS systems? The introductory lecture aims to vitalize one of the most traditional topics in the IWA World Conferences on Anaerobic Digestion.

Despite the promise of anaerobic biotechnology, its full-scale application to treat certain organic waste streams and recover resources remains limited, suggesting that new approaches are needed to expand its use. This presentation will show the development of new anaerobic bioprocesses by applying knowledge of microbial community structure and function and sustainable technology design practices. This approach will be illustrated by focusing on anaerobic dynamic membrane bioreactor development for treating waste streams containing recalcitrant lignocellulosic compounds.

The thermodynamic end-product of the anaerobic digestion process is methane containing biogas, but many research efforts aim for other products, like volatile fatty acids (VFA), molecular hydrogen, ethanol or lactate. These products represent a higher value in a biobased economy when recovered directly from the fermentation broth or when converted in secondary bioprocesses for the production of medium chain length fatty acids or bioplastics. A prerequisite for development of these processes is the (controlled) absence of methanogenesis to maximize the product yield. In this presentation I will describe how and why product formation in anaerobic fermentations depends on the cultivation conditions imposed. Emphasis will be on the identification of key environmental switching points that determine if (partial) inhibition of methanogenesis will be achieved. To which extent these switching points are independent of the history of the microbial community will be a topic of discussion.

The traditional methods of treating urban wastewater are energy-intensive and contribute to carbon emissions. Anaerobic digestion technologies can be used to reverse the negative energy balance of wastewater treatment. By treating municipal organic waste and wastewater together, energy recovery can be further enhanced. The integration of various emerging concepts in this integrated waste management concept, such as carbon redirection, anaerobic membrane bioreactor, lithotrophic denitrification, post-ozonation, and artificial methane production, holds significant promise for resource recovery and sustainability. This integrated concept will also support the resilience of the urban water supply system against global warming by providing reclamation and reuse of high-quality treated wastewater in dual water distribution networks. A holistic approach that includes these emerging technologies in municipal organic waste and wastewater treatment will be explored in this presentation.

Microbes play a crucial role in facilitating the green transition towards sustainable and eco-friendly practices. This abstract presents various ways in which microbes contribute to develop technologies for the transition from the fossil based economy to bioeconomy. Microbes are are involved in bioremediation, where they break down and detoxify pollutants in contaminated sites, helping restore ecosystems affected by human activities. Additionally, certain microbes possess the ability to produce biofuels and biochemicals, offering a renewable alternative to fossil fuels and reducing greenhouse gas emissions. Furthermore, microorganisms contribute to sustainable treatment of organic waste. Biotechnologies are contributing to valorisation of residual resources, promoting efficient recycling and nutrient cycling.

In this presenation I will show potential applications from biogas to biomethane which can be supplied to the natural gas grid. Methane can also be used as substrate for cultivation of methanotrophic bacterial with high protein content with good aminoacids composition. Additional products can be obtained from the intermediates of the AD process, such as PHAs or specific volatile fatty acids, alcohols, lactic acids etc. Results of several of these alternatives to heat and electricity will be presented. Current status and future opportunities will be discussed.