Wastewater reclamation

and re-use

 

 

Urbanization and continuous population growth have led to  constantly increasing demand of fresh water, which in turn results in significant wastewater disposal to surface recipients. This seriously threatens both natural and human environment. Therefore wastewater reclamation appears to be an attractive solution for the sustainable management of water resources confronting with the problems rising from climate change and drought.

Τhe term water re-use) is used to describe the beneficial use of treated wastewater. According to US Environmental Protection Agency (EPA) water re-use is defined as reusing treated wastewater for beneficial purposes alternating from one application to another (such as agricultural and landscape irrigation, industrial processes, toilet flushing, and replenishing a ground water basin, referred to as ground water recharge). Water recycling refers to the internal utilization in the same application.

In Greece there is relevant legislation (Common Ministerial Decision 145116/2001) for the re-use of biologically treated wastewater for irrigation purposes. Two types of irrigation are specified, based on the type of cultivation, the irrigation system and the public accessibility

Limited irrigation which involves industrial crops, non-fruit trees, meadows, etc and unlimited irrigation which includes vegetables for human consumption, vineyards, grass, fruit trees, etc. Both types require a different degree of wastewater treatment.

 

Sewage sludge

management

 

 

Operation management and process optimization of wastewater treatment plants

 

 

 

During wastewater treatment significant amounts of biological sludge and other by-products (screenings, grit) are produced. A crucial issue which rises among the stakeholders is the safe and environmentally acceptable management of this sewage sludge.

Sludge produced in wastewater treatment plants is subjected to additional treatment in order to:

• reduce the water content for economic treatment

       and disposal costs

• stabilize the final product
• remove all pathogens

Common Ministerial Decision 50910/2727/2003 harmonizes the European Code of Solid Waste in Greek legislation. According to this Code all types of municipal sludges are included in Chapter 20. Municipal wastes. With the same Decision the National Planning and Management of non-hazardous wastes such as sewage sludge, is defined.

Its aim is to achieve the highest level of exploitation so as to minimize the quantity of the finally disposed sludge.

Sludge management techniques include:

• agricultural applications as fertilizer
• rehabilitation of impaired soils
• drying and use as combustible material
• disposal to landfills
• anaerobic digestion for production of thermal and/or electric energy
• composting

Sludge must be further treated before being used in agriculture.

The use of sludge must be prohibited for use on:

• grassland or forage crops if the grassland is to be grazed or the forage crops to be harvested before a certain period has elapsed.
• soil in which fruit and vegetable crops are growing, with the exception pf fruit trees.
• ground intended for the cultivation of fruit and vegetable crops which are normally in direct contact with the soil and normally eaten raw, for a period of 10 months preceding the harvest of the crops and during the harvest itself.

Biological treatment of wastewater is a dynamic process which involves mechanical, biological, chemical, and human elements, all of which must fall within in the correct range of values for the treatment system to be effective and reliable. In order to control and monitor such a plant successfully and achieve all effluent requirements, the operator should be familiar with all biological and chemical processes involved and  be capable to intervene in emergency situations and optimize the system’s efficiency.

Crucial control parameters are:

• Influent wastewater quality characteristics
• Influent flow volume
• Dissolved oxygen concentration in the biologic reactor
• Mixed liquid suspended solids in the biologic reactor
• Waste activated sludge quantity
• Microscopic monitoring of activated sludge microorganisms in the biologic reactor

Custom effluent parameters  to monitor are usually specified in environmental licenses,   based on Commission  Directive 91/271/EEC, and may be BOD5, COD, SS, TN, Ammonia, temperature, pH, etc.

They are most depended on the type of the effluent receptor (river, sea, soil, irrigation, etc)

According to the same Directive the minimum annual number of effluent samples should be:

2.000- 9.999 e.p        12 samples the first year

10.000-19.999 e.p      12 samples

>50.000 e.p.              24 samples