The use of anaerobic digestion for wastewater treatment continues to be increasingly valued due to the need for resource preservation and recovery. Different high-rate anaerobic reactors with biomass retention capacity exist for the treatment of industrial and municipal wastewaters. The anaerobic moving-bed biofilm reactor (AnMBBR) is a newer anaerobic reactor that operates with biofilm growing on mobile inert media. It is simpler in design and operation compared to other high-rate reactors and it can withstand high concentrations of suspended solids. The number of studies on AnMBBRs for wastewater treatment has been increasing; however, until now no systematic evaluation of the scientific literature on this topic exists. This review aims to identify the types of wastewaters treatable using AnMBBRs, the process configurations for best treatment performance, and advantages/disadvantages of AnMBBRs.

AnMBBR is suitable for wastewater treatment at high organic loads, as it allows for high volumetric loading rates and short retention times, resulting in a compact system. It can tolerate large variations of organic and hydraulic loads and even starvation periods. This flexibility makes AnMBBR a suitable option for the treatment of industrial wastewaters experiencing seasonal variability in production levels or changes in product lines. Overall, AnMBBR technology is a versatile and effective option for the treatment of various wastewaters, offering high removal efficiencies, stability, and flexibility in operation, even at temperatures lower than the typical mesophilic range used in anaerobic treatment. Its potential for application is expected to continue growing along the need for resource recovery from wastewaters.

Waste management has been developing in response to needs. The need to get rid of unwanted materials has always been a motivation but using the resource value of waste has also been a driver from the stone age and forwards. In affluent times not so much. Sanitation became a motivation with the discovery of pathogenic microorganisms in the mid-19th century, and after World War 2 (WW2) a strong focus on environmental protection developed, and in recent times, the resource aspect has received an interest despite material affluence. Legislation has been one of the drivers for recent developments, in the case of Sweden, the environmental protection legislation came in the late 1960s, and a few years later, the municipalities got the exclusive right to collect and manage household waste. Many local and regional waste management companies were established, owned by the municipalities. These organizations became agents of development, due to the increased scope and capacity. Adding to the environmental protection agenda, a renewed interest in waste as a resource was initiated by the oil crises of the 1970s, resulting in new waste incineration plants, with energy recovery, connected to already existing district heating networks. Mistakes, failures and alarms in the 1970s and the 1980s resulted in treatment method improvements and the establishment of source separation as an integral part of waste management. The waste management community stands strong today and is taking a more proactive role than before, which includes a stronger focus on communication with other stakeholders.

The use of anaerobic moving-bed biofilm reactors was investigated for biogas production from the liquid fraction of sewage sludge hydrolysate. Anaerobic digestion requires traditionally long retention times due to the slow growth of methanogens. This work investigated biogas production with 2–3 days retention time under mesophilic (37°C) and thermophilic (50°C) conditions. Two continuous reactors were operated to treat the liquid fraction of hydrolysate sewage sludge for 196 days. The mesophilic reactor showed a more stable performance compared to the thermophilic one. The mesophilic reactor kept the soluble COD removal above 80 % at a volumetric loading rate (VLR) above 7 g COD L⁻¹ d⁻¹, and specific surface loading rate (SARL) above 20 g SCOD m⁻² d⁻¹. In contrast, the thermophilic reactor displayed a soluble COD removal above 80 % at an average VLR of 4.2 g COD L-1 d-1, and average SARL of 14 g SCOD m⁻² d⁻¹. The biogas from both systems contained 73 % methane. The microbial analysis of the biofilm showed that 36 % of the viable cells were anaerobic microorganisms.

This project has targeted utilisation of infrastructure for organic waste treatment in Sweden, in particular sewage sludge, to achieve increased production of high-value materials and energy carriers, reduced use of primary resources, and improved economic performance. We have investigated the sewage sludge management system as a socio-technical system facing a change, with integral connections to the energy and waste systems.

In conclusion, there is no silver bullet for the future of sewage sludge management. Indeed, it would have to be a full clip of silver bullets, as we found that a mishmash of different barriers –technical, economic, legal, and related to public perception – creates uncertainty that hinders progress regarding both sustainable long-term strategies and technological advancement. The Swedish sewage sludge management is largely fragmented, highlighting the need to shift directionto a more holistic approach. This can help actors address common issues rather than focussing solely on activity-specific problems. Introducing new legislation could be a key step, as the current specific legislation on sewage sludge has a seemingly insignificant role for today’s sludge management, compared to other legislation and the voluntary certification.

We have formulated six overall research highlights, to outline both published results and meta-conclusions based on combined insights. Each highlight is described separately in this report.

This study uses a new approach for the recycling of plant nutrients by co-digesting sewage sludgewith fly ash from a wood combustion. Sewage sludge and fly ash both are enriched with nutrientsof the wastewater resp. wood, which makes these products an enhanced source for recycledfertilizers. The effects of the ash addition to the anaerobic digestion are studied in several labscale experiments including effects on the gas production and microbial activity. Following that,the fertilizing qualities of the digestate are evaluated by plant growth experiments. The resultsshow that the fertilizing qualities of the digested sludge were improved by the ash addition.Next to this, gas production results show that the methane production was not affected by theash addition, while the total gas release was reduced. The sulphur addition by the ashstimulated sulphate reducing bacteria. The sulphate reducing bacteria did not markedly inhibitthe methanogens.

A statistically designed range of tests was used in order to map the impact of time, temperature and pH on the acidogenic fermentation of sewage sludge with the addition of waste fly ash. The main factors investigated were temperature (35, 55 and 65 °C), pH (7, 8 and 8.5) and retention time (1, 2 and 4 days). The initial pH was adjusted by adding ash. Up to about a third of the volatile solids could be solubilized in less than two days retention time. Higher temperatures (55 and 65 °C) and adjusted pH (7 and 8) favored hydrolysis whereas fermentation producing organic acids was faster at lower temperatures (35 °C). Sludge hydrolysis occurred fast at 55 and 65 °C, reaching a solubilized total organic carbon (TOC) concentration of 3.84 g TOC L^-1 after one day. Thermophilic conditions (55 and 65 °C) resulted in a lower volatile fatty acids (VFA) concentration compared to mesophilic conditions (35 °C). At 35 °C, the highest VFA concentration was measured after 4 days and initial pH 7 (10.0 ± 0.2 g COD L^-1). This study showed the potential of using a waste stream to increase and hasten the hydrolysis of particulate organics, resulting in higher TOC solubilized in 2 days, while promoting a higher VFA production measured as g COD L^-1.

As the resource recovery from mixed waste streams are performed, new mixed waste streams are generated. Some of these waste streams does not fit well to existing waste management options, for example, they may hold a to low heating value to sustain combustion and they may have a too high carbon content to be accepted at non-hazardous landfills. Also various health and pollution risks may arise as well as practical handling issues due to the physical properties of such wastes. One such waste is the under sieve fraction generated when recovering metals and fuel from mixed waste streams using mechanical and magnetic separation tools. Such mechanical sorting is typically used for mixed wastes of different properties and particle sizes, such as houshold bulky wastes, construction and demolition waste, and at landfill mining materials. In this work, we examine the properties of one case of mechanical sorting of bulky wastes, including construction and demolition wastes. We analyse a broad spectrum of chemical, physical, and mechanical properties as well as some biological. Based on the data we develop recommendations for landfilling, what potential problems might arise and how to counteract them.