Sludge produced by municipal wastewater treatment plants (WWTPs) amounts to only a few percent by volume of the processed wastewater, but its handling accounts for up to 50% of total operating costs. Moreover, the need to achieve a sustainable sludge management strategy has become of great concern. It follows that as conventional and more traditional options, such as land spreading for agricultural purposes, are progressively restricted, and often legally banned, the development of innovative systems to maximize the recovery of useful materials and/or energy is required. A change toward more sustainable procedures can be promoted through an integrated approach, including the assessment of management routes capable of maximizing the recycle/recovery benefits, through low energy impact systems, and the development of operational systems appropriate to local circumstances. Based on the above considerations, an integrated system is proposed in this paper. It includes Anaerobic digestion, Dewatering/Drying, and Pyrolysis/Gasification processes which are efficiently coupled for the recovery of products for material reuse and/or energy purposes. Such an integrated system should also allow the recovery of one or more materials, depending on the combination of processes which best fit specific local situations.

For carrying out sludge lab-scale tests, and interlaboratory trials for standards validation, the availability of samples with “certified and constant” characteristics is required. When “dried sludge” samples cannot be used, problems arise because (i) most fresh sludge characteristics change with storage time, also because some preservation practices are not applicable or their effects unknown, (ii) some fresh sludge characteristics are strongly affected by handling, and (iii) fresh sludge requires particular precautions and authorization for transportation. This means that using “fresh sludge” samples cannot guarantee reliability and reproducibility of results, so a valid alternative consists in testing “synthetic suspensions” samples to be on-site prepared. This should also give the possibility to compare results obtained in different places and times. Within this framework, Task Group 3 (TG3) of Working Group 1 (WG1) of Technical Committee 308 (TC308) of European Standardization Committee (CEN) undertook the preparation of a Technical Report dealing with the preparation of synthetic suspensions, both inorganic and organic, in repeatable conditions, able to describe the behaviour of a real sludge. This paper discusses a proposal for ingredients and modalities to prepare such synthetic suspensions that will be systematically tested in already planned lab experiments to define an optimal recipe.

One of the issues facing modern society, regardless of the socio-economic level of the communities involved, is the development of sustainable strategies for the management of sludge/biosolids. Nowadays, it is imperative to replace solutions aimed at simply “disposing of” with those oriented toward “maximizing recovery benefits”. It is desirable that agricultural use remains the main option in sludge/biosolids management; however, to ensure effective and safe agronomic benefits, correctly fulfill the legal requirements, and build stakeholder and public confidence, rigorous and sustainable procedures need to be established. The development of realistic and enforceable regulations is crucial, as they represent the right balance between the different aspects of coordinated and effective management. Furthermore, it is important to recognize that regulations must be supported by standardized characterization procedures and good practice guidelines because well-defined procedures allow the legal requirements to be correctly and uniformly met, as well as to reliably compare the results obtained under different conditions and their wide application in different regulatory contexts. In this article, the main aspects for (i) the sustainable application of sludge/biosolids in agriculture and (ii) the development of standardized characterization methods and procedures, thus ensuring effective agronomic benefits and guaranteeing quality/safety of agricultural products, are discussed. Some pieces on the evolution of European legislation in this field are also provided. Details and results of the research activities behind the development of these methods/procedures can be found in the referenced documents.

Sustainable procedures for sludge/biosolids management require the development of strategies to reduce the amount of sludge to be handled and to produce higher quality biosolids. Therefore, realistic and enforceable regulations adapted to local situations must be developed, defined outlet procedures established and good quality products guaranteed. To this end, the definition of standardized characterization procedures and guidelines for good practices becomes a necessary support to regulations. To contribute to the development of the EU directives dealing with sludge, the European Committee for Standardization (CEN) has established Technical Committee 308 (TC 308) whose scope is the standardization of methods for sludge characterization and the production of guidelines of good practice. In this paper, the most recent developments of the CEN/TC 308 work for the chemical, biological and physical characterization of sludge/biosolids are discussed in relation to the main different treatment and outlet options.

Sludge management is one of the critical issues facing modern society due to the fast increase in its production as a result of extended sewerage, new work installations and up-grading of existing facilities. In order to (i) properly perform the utilization and disposal operations, (ii) correctly fulfil the legal requirements and (iii) build stakeholder and public confidence, it will be necessary to establish defined outlet procedures/routes and guarantee a good sludge quality. Therefore, characterization to evaluate sludge chemical, biological and physical properties is a necessary tool in sludge management. However, characterization procedures often specify different methodologies, materials and accessories; so results obtained in different places may not be fully reliable. Also comparison of the results can be problematic because they have not been obtained under standardized conditions. Consequently, the development of standardized validated characterization methods and procedures becomes necessary too. Further, the development of standardized characterization methods and procedures should be supported by the preparation of 'guidelines' of good practice for the different options of sludge use and disposal in order to give guidance to producers/users on how to meet legislation requirements and perform sustainable operations. In this paper the main parameters for sludge characterization are discussed and developments in European standardization outlined.