Mechanical disintegration can be used for an accelerated and improved anaerobic digestion of excess sludge. The hydrolysis is the limiting step of this process. Mechanical disintegration can be used to disrupt the cell walls and to cause the release of the organic material from the cells. Particle size analysis describes the size reduction but is not suitable for characterising the release of the organic material and the cell disruption. Two biochemical methods were developed for these phenomena. One of the parameters provides information about the disruption of micro-organisms, the other one gives information about the release of organic material. Different ultrasonic homogenizers, a high pressure homogenizer and stirred ball mills were used for disintegration experiments using various parameters. The influences of a mechanical disintegration on the particle size and of the energy intensity on the disintegration were investigated. Further investigations had to detect the influence of the solid content on the disintegration results. For sludge with a higher solid content better results in terms of energy consumption could be achieved. An optimum of the bead diameter and the stress intensity in stirred ball mills could be detected. A comparison of the results of different methods of sludge disintegration shows that the investigated ultrasonic homogenizers are inferior to a high pressure homogenizer and a stirred ball mill in terms of energy consumption.
Wastewater management in Latin America faces great challenges to reach a sustainable state. Although enough infrastructure has been built to treat around 40% of wastewater, only between 15–20% is effectively treated, and abandoned or defective infrastructure is a common sight. Data about current conditions at specific sites is quite fragmented, when existing. This leads to challenges in management, decision making and planning for sustainable options. We argue that a main obstacle is the lack of a regionally relevant sustainability assessment framework that allows for a holistic understanding of wastewater management as a nexus problem. We therefore developed a comprehensive framework to (1) understand current conditions (2) involve stakeholders and (3) point to pathways to improve wastewater management in the Americas. Building on literature review and stakeholder involvement, we constructed a multi-scalar extended dataset framework that is adaptable to different study sites using specific criteria. Sustainability was assessed through a “distance-to-target” approach. Social and economic variables were the lowest ranking in both cases, with technical variables generally performing better. Although some dimensions of sustainability are performing acceptably, others, such as social and economic, are general low to very low performing. This means, when looked at in an integrated manner, neither of the wastewater management systems analysed can be considered sustainable. Here we present the approach itself, the results of its application in two pilot sites in Latin America, and our recommendation to shift waste water management into sustainability.
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