Suchergebnisse

Activated sludge is now one of the most widely used biological processes for the treatment of wastewaters from medium to large populations. It produces high amounts of sewage sludge that can be managed and perceived in two main ways: as a waste it is discharged in landfill, as a fertilizer it is disposed in agriculture with direct application to soil or subjected to anaerobic digestion and composting. Other solutions, such as incineration or production of concrete, bricks and asphalt play a secondary role in terms of their degree of diffusion. The agronomical value of domestic sewage sludge is a proved question, which may be hidden by the presence of several pollutants such as heavy metals, organic compounds and pathogens. In this way, the sustainability of sewage sludge agricultural disposal requires a value judgment based on knowledge and evaluation of the level of pollution of both sewage sludge and soil. The article analyzed a typical Italian case study, a water management system of small communities, applying the criteria of evaluation of the last official document of European Union about sewage sludge land application, the "Working Document on Sludge (3rd draft, 2000)". The report brought out good sewage sludge from small wastewater treatment plants and soils quality suggesting a sustainable application.

Cover title: Wastewater treatment facility needs ; Mode of access: Internet.

ABSTRACTTHE 'root‐zone' sewage‐treatment proccess was introduced to the UK and Yorkshire Water in 1984, with claims that capital and operating costs were significantly less than for conventional processes. The design and construction of the experimental root‐zone bed at Holtby (which forms part of Yorkshire Water's contribution to the evaluation of the process in the UK), is described. The planting of the Phragmites, their growth and the performance of the bed are discussed. Suspended solids and BOD removal efficiencies have satisfied the predictions of the designers for the performance of a bed which is still immature, although ammonia and phosphate removals have been low. The role which is played by the reeds is considered to be minor, and it is suggested that it is too early to judge the Holtby bed either a success or a failure. The paper also discusses the problem of weed control, the importance of floor slope, maturity of the system and the use of gravel instead of soil.

The current situation on the quantities and disposal methods of sewage sludge in European Union is discussed, together with the trends up to 2005 and the future sludge disposal possibilities. The problems relating to the methods currently used in Greece and the requirement for land suitable for the safe agricultural application of sewage sludge are evaluated. This concept will be important to the decisionmakers for the purpose of the disposal of sewage sludge in the future. Soil measurements in lands used for sludge disposal in western and southern Greece show that some soils have been already polluted by heavy metals and should be abandoned while others need careful monitoring until their saturation.

AbstractThere is a significant amount of energy in the carbonaceous component of sewage sludge. Effective use can be made of this energy through conversion to the gaseous state followed by gas cleaning and subsequent firing of a gas turbine.This paper (a) compares the technology for the gasification of dried sewage sludge, noting the advantages in favour of fuelling a gas turbine, (b) reviews the significance of the individual components in sewage sludge, and (c) provides a brief introduction to a demonstration project which was embarked upon by Northumbrian Water in conjunction with Lurgi, with the financial support of an ECU Thermie Grant.