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This paper reports a synthesis of policy-relevant evidence on household waste prevention, based on a UK portfolio of primary research and a broad international review. Waste prevention was defined as strict avoidance, reduction at source (e.g. home composting) and reuse (for the product's original purpose) - recycling was excluded. A major focus was on consumers. Waste prevention is not one but many behaviours; the review revealed a general hierarchy in their popularity, from donating goods to charity at the top; through small reuse behaviours around the home; to activities involving changes in consumption habits at the bottom; one estimate is that 60% of the public does at least one of these activities, some of the time. Barriers to engaging householders include both modern consumer culture and a genuine confusion that waste prevention is equivalent to recycling. The public can be engaged through local or national campaigns, with a wide range of interventions and communications approaches available. On the products and services side, the primary opportunity within the scope of the review was identified as increasing reuse. The barriers included operational difficulties (funding, capacity, logistics) and consumer attitudes towards second-hand goods. The main opportunities are to ensure more strategic planning for reuse by local authorities and better co-ordination and joint working with the third sector. The review examined the impact or potential of various policy measures designed to influence household behaviour directly or the products and services provided to them. Overall, the international evidence suggests that waste prevention benefits will be derived from a 'package' of measures, including, for example, prevention targets, producer responsibility, householder charging, funding for pilot projects, collaboration between the public, private and third sectors, and public intervention campaigns. UK evidence suggests that the greatest tonnage diversions can be achieved on food waste, home composting and bulky waste. The principal evidence gaps relate to robust and comprehensive quantitative data. Better evidence is needed of what actually works, and what outcomes (weight, carbon and costs) can be expected from different measures. More sensitive and effective monitoring and evaluation is needed to provide the evidence required to develop the necessary basket of future policy measures at local and national level.

This paper presents one strand of the findings from a comprehensive synthesis review of the policy-relevant evidence on household waste prevention. The focus herein is on how to measure waste prevention: it is always difficult to measure what is not there. Yet reliable and robust monitoring and evaluation of household waste prevention interventions is essential, to enable policy makers, local authorities and practitioners to: (a) collect robust and high quality data; (b) ensure robust decisions are made about where to prioritize resources; and (c) ensure that waste prevention initiatives are being effective and delivering behaviour change. The evidence reveals a range of methods for monitoring and evaluation, including self-weighing; pre- and post-intervention surveys, focusing on attitudes and behaviours and/or on participation rates; tracking waste arisings via collection data and/or compositional analysis; and estimation/modelling. There appears to be an emerging consensus that no single approach is sufficient on its own, rather a 'hybrid' method using a suite of monitoring approaches - usually including surveys, waste tonnage data and monitoring of campaigns - is recommended. The evidence concurs that there is no benefit in trying to further collate evidence from past waste prevention projects, other than to establish, in a few selected cases, if waste prevention behaviour has been sustained beyond cessation of the active intervention campaign. A more promising way forward is to ensure that new intervention campaigns are properly evaluated and that the evidence is captured and collated into a common resource.

This paper presents one strand of the findings from a comprehensive synthesis review of policy-relevant evidence on household waste prevention. Understanding what is achievable in terms of local household waste prevention intervention campaigns enables policy makers, local authorities and practitioners to identify optimum approaches to deliver effective behaviour change. The results of the evidence have been assembled and are discussed in two contexts: (1) the delivery of intervention campaigns as a package of measures used to 'enable', 'engage' and 'encourage' householders to change their behaviour; and (2) the impact of local household waste prevention intervention campaigns in terms of tonnage data. Waste prevention measures adopted include home composting, reducing food waste, smart shopping, donating items for reuse, small changes in the home, reducing junk mail and using cloth/reusable nappies. In terms of diverting biodegradable municipal waste from landfill, the biggest impacts can be attributed to food waste prevention (1.5 kg household(- 1) week(-1)) and home composting (2.9 kg household( -1) week(-1)). Projects providing a package of other waste prevention interventions have shown a very wide range of impacts: a broad indication is that such a package could achieve around 0.5 to 1 kg household(-1) week(- 1) reduction at source. Disaggregating which waste prevention measures influenced uptake is generally not possible, but the evidence suggests that this does not matter: behaviour change has been supported by integrating a range of intervention tools and campaign promotions which have made a collective rather than isolated difference: it is a collection and an accumulation of measures that will have impact.

There is a well-documented interest in how insights from the study of complexity can be applied to policy evaluation. However, important questions remain as to how complexity is understood and used by policy evaluators. We present findings from semi-structured interviews with 30 UK policy evaluators working in food, energy, water and environment policy domains. We explore how they understand, use and approach complexity, and consider the implications for evaluation research and practice. Findings reveal understandings of complexity arising from contextual factors, scale-related issues and perceptions of unpredictability. The evidence indicates terminological and analogical use of complexity and its concepts by policy evaluators, but limited evidence of its literal use. Priorities for the future include framing complexity more pragmatically and as an opportunity not a cost. Communicating this up the policy hierarchy is the key to progressing complexity-appropriate evaluation – this can be enabled by strengthening links between policy evaluation and academic communities.

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A study was performed based on the design of a new wastewater treatment plant (WWTP) to be built in Weesp, The Netherlands (about 46,000 Population Equivalents (PE)). The conventional activated sludge plant was considered among the alternatives, with and without primary sedimentation. This pre-treatment technique is considered a sustainability measure as it improves the energy balance of the WWTP. However, at the same time, the question arose about the cost effectiveness of this measure. The scope of the study was to assess whether other sustainability measures (like solar panels) can realise the same level of sustainability with lower costs. The outcome of the study indeed shows that, for a new WWTP, it is considerably cheaper to avoid primary sedimentation and focus on other measures like solar panels instead. This appeared not only to be the case for the scale of WWTP Weesp, but also for WWTPs with capacities higher than 500,000 PE. For existing WWTPs with primary sedimentation, the choice can be different as customisation is necessary.

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