Sludge disposal amd management

 Sludge disposal: -

Abstract :-

Sludge management is one of the most difficult and challenging tasks of wastewater treatment plants due to its high water content and poor dewaterability and strict regulation for sludge reuse or disposal. One of the recent goals of wastewater treatment plants is to develop more environmentally friendly processes to reduce the volume of sludge for disposal and to convert sludge into bioenergy. Energy recovery of the sludge generally includes the conversion of the sludge into biogas, syngas, and bio-oil which can be further converted into electricity, mechanical energy, and heat. In this chapter, methods for energy recovery from wastewater sludge in the forms of bio-oil and biogas are reviewed. An overview of different sludge types and the common methods for measuring their characteristics and bio-oil production from sludge through hydrothermal treatments are discussed. Hydrothermal treatment reaction pathways and the effects of various operating parameters such as reaction temperature and time, the presence of a catalyst, feedstock type, water-to-biomass ratio, and water at sub −/supercritical conditions are discussed. In addition, some available hydrothermal processes in pilot or demonstration scales are introduced. Biogas production from sludge through anaerobic digestion is also reviewed, and effects of various pretreatment methods such as thermal, chemical, thermochemical, and mechanical treatments on the anaerobic digestion performance and the final biogas yield are discussed. Furthermore, the established and emerging technologies for each pretreatment method are introduced. 

Introduction

Sludge disposal :- The solids that result from wastewater treatment may contain concentrated levels of contaminants that were originally contained in the wastewater. A great deal of concern must be directed to the proper disposal of these solids to protect environmental considerations. Failure to do this may result in a mere shifting of the original pollutants in the waste stream to the final disposal site where they may again become free to contaminate the environment. A more reasonable approach to ultimate solids disposal is to view the sludge as a resource that can be recycled or reused.

All the sewage sludge produced at a treatment plant must be disposed of ultimately. Treatment processes such as have been described may reduce its volume or so change its character as to facilitate its disposal, but still leave a residue which in most cases must be removed from the plant site. Like the liquid effluent from the treatment plant, there are two broad methods for the disposal of sludge - (1) disposal in water, and (2) disposal on land. This applies regardless of whether or not the sludge is treated to facilitate or permit the selected method of disposal. 

Methods for sludge disposal :-

1.   Disposal in water :- This is an economical but not common method because it is contingent on the availability of bodies of water adequate to permit it. At some seacoast cities, sludge either raw or digested is pumped to barges and carried to sea to be dumped in deep water far enough off shore to provide huge dilution factors and vent any ill effects along shore.

In the past few years there has been an increased problem of pollutional loads, well above safe standards, affecting the south-shore beaches on Long Island, facilitating the closing of the beaches to the public. Some of these pollutional loads have been attributed to sludge deposits coming to shore form off-shore ludge barging operations. Where barged to sea, the value of some treatment such as thickening or digestion, depends on the relative cost of the treatment and savings in cost by barging smaller volumes, or the value of gas produced by digestion.

2.  Land filling:- A site for the disposal of waste materials by burial and is the oldest form of waste disposal. 

         Some landfills are also used for waste management purposes,      such as the temporary storage, consolidation and transfer, or processing of waste material (sorting, treatment, or recycling).

        Problem with this method is that many landfills are filling up,    and towns are having trouble finding places to put new ones.

(3) Composting :- Composting can be defined as the aerobic thermophilic decomposition of organic wastes to a relatively stable humus. Decomposition results from the biological activity of microorganisms which exist in the waste. A good compost could contain up to 2 percent nitrogen, about 1 percent phosphoric acid, and many trace elements. Its most valuable features, however, are not its nutrient content, but its moisture retaining and humus forming properties. Many types of microorganisms are involved in converting the complex organic compounds such as carbohydrates and proteins into simpler materials, but the bacteria, actinomycetes, and fungi, predominate. These organisms function in a composting environment that is optimized by copying the natural decomposition process of nature where, with an adequate air supply, the organic solids are biochemically degraded to stable humus and minerals. Compost is generally considered as a material to be used in conjunction with fertilizer, rather than as a replacement for fertilizer unless it is fortified with additional chemical nutrients.

Compost benefits the soil by replenishing the humus, inmproving the soil structure, and providing useful nutrients and minerals. It is particularly useful on old, depleted soils and soils that are drought-sensitive. In horticulture applications, compost has been useful on heavy soils as well as sandy and peat soil. It has been commonly applied to parks and gardens because it increases the soil water absorbing capacity and improves the soil structure.

Parameters: All composting processes attempt to create a suitable environment for thermophilic facultative If the environmental conditions for biological aerobic microorganisms. decomposition are appropriate, a wlde variety of organic wastes can be composted. The most important criteria for successtul composting are: 

(a) complete mixing of organic solids, 

(b) nearly uniform particle size, 

(c) adequate aeration, 

(d) proper moisture content, 

(e) proper temperature and pH, and

         (f) proper carbon-nitrogen ratio in the raw solids.

(4) Other methods :- 

Ocean Disposal - Dumping or controlled release of sewage sludge from a barge or other vessel into marine water. 

Distribution and Marketing - The give-away, transfer, or sale of sewage sludge or sewage sludge product in either bagged or bulk form. 

Surface Disposal - A controlled area of land where only sewage sludge is placed for a period of one year or longer. Sludge placed in this area is not provided with a daily or final cover. 

CONCLUSION:- 

Nothing is waste until you cannot use it anymore in anyway! At one time, wastes piled up and people did not think deep enough on how to use them. Today, it is gratifying to see the innovations in waste management - recycling wastes into usable products, generating methane for fuels, manufacturing new products for home/commercial usage such as fence posts, furniture… the list goes on. These are conclusions for waste management most important being ‘promoting brain power.’ 

(Thanks you)