A review of the sustainable value and disposal techniques, wastewater stabilisation ponds sludge characteristics and accumulation

Based on worldwide works available in international literature, this paper describes the status of sewage sludge resulting from settleable solids in waste stabilisation ponds (WSP). This review presents, in detail, sludge characteristics, production and accumulation rates in order to provide background information to those who expect to advise or get involved with sewage disposal in situations where resources are limited. Knowing that several years are usually required for a sludge removal operation and that the long-term sustainability of WSP systems is dependent on the safe and effective management of their sludge, its cost must be estimated and taken into account in the annual maintenance costs of the processes. Thus, this paper intends to summarise desludging methods and their financial estimation. Even when ponds have been functioning for several years, most of the sediments are stabilised well, the final disposal is an issue in terms of risk due, for example, to their content in nematode eggs. More generally, the pathogen content in sludge from WSP ponds has to be known to define an appropriate management and to safeguard public health. Based on existing data, the rates and distribution of helminth eggs will be presented and practical treatment methods will be suggested. A number of sludge utilisation and disposal pathways will also be summarised. Sludge activity in terms of oxygen consumption is also discussed in order to gather more information to improve pond design and keep an economic and sustainable value of WSP. The objectives of the present review are to advance knowledge and gather scientific and technical information on all aspects of sludge management including production, characterisation, management, agricultural reuse and ultimate disposal.     

Mercury cleanup: The commercial application of a new mercury removal/recovery technology

Efficient, economical treatment of mercury-contaminated soils and industrial wastes requires a treatment process that reduces mercury content to near background levels (<1 ppm) and recovers the removed mercury in pure recyclable form without producing liquid, solid, or gaseous secondary wastes. This article reviews the results achieved using a medium-temperature thermal desorption process developed and commercialized by Mercury Recovery Services, Inc. (MRS) that has successfully achieved these goals.     

Zur Morphologie,Histochemie, Tagesperiodik und Biologie der Operculardrüse bei Labriden und Scariden (Pisces)

A mucous gland is described, which is responsible for the production of the slime envelope in scarids and labrids. For this gland the name ‘opercular gland’ is suggested. The gland is developed, to a greater or lesser extent, in most of the genera examined. Morphological and histochemical studies indicate that the form of the gland is characteristic of the genus. Labrids and scarids can be divided, histochemically, into 3 groups: (1) opercular gland secretes only neutral MPS; (2) opercular gland secretes both neutral and weakly acidic MPS; (3) opercular gland secretes neutral MPS, weakly acidic and strongly acidic MPS (the strongly acidic MPS are probably sulphated). Species are found in all 3 groups with granular cells which secrete a tyrosine containing glycoprotein. The fish can be made to produce the mucous envelope by stimulation of the parasympathetic nervous system using pilocarpine. It is, therefore, assumed that the gland is controlled by the nervous system. Morphological studies of the gland show that the mucous is normally synthesised only in the evening, i.e. when it is needed; no storage takes place. Continuous light experiments have shown the gland to possess an endogenous rhythm of the same frequency as the fish's activity rhythm. Even those labrids which sleep under sand produce mucous. The average area of the longitudinal section of an opercular gland cell is more than 500 µ² in those species which produce a complete envelope, and usually somewhat less in the other species examined. The possible importance of the opercular gland in taxonomical and phylogenetical studies is discussed.