The sludge represent the waste product of a solid any purification cycle (biological, chemical, physical etc..) That must be collected and treated before being disposed.
The main treatments of sludge are:
– Thickening: has the function of removing large quantities of the water contained in the sludge, thereby reducing the volumes in favor of the treatments provided downstream of the sludge line.
– Biologic Stabilization : It is a complex metabolic processes through which the putrescible organic content of the sludge from the primary and secondary sedimentation tanks is transformed into simpler stable substances. The digestion can be of two types, aerobic and anaerobic digestion, and the product wherein the digestion occurs are called digesters.
-Conditioning: It is used before a treatment of mechanical dehydration and serves to improve the filterability of the sludge.
– Dehydration: This is used to reduce further the water content of the digested sludge. May be natural (for natural drying on drainage beds) or mechanical (filter pressing tape pressing and centrifugation).
A further treatment of dehydration of the digested sludge can be the heat treatment for drying or incineration (although it is a method of dehydration, it is used for the disposal of sludge).
The demineralization is a chemical-physical treatment, usually of water, for total (zero liquid discharge) or partial elimination of dissolved salts.
The water, as a common fluid with high transport capacity of heat (the latent heat of vaporization of water is the highest known with the exception of the ammonia) is frequently used for the transmission of energy, in the form of heat.
This involves the supply of thermal energy to water, and possibly a change of physical state. In these phases you can have separation of dissolved salts in the water itself, which then precipitate deposited on the exchange surfaces.
salt deposits on the surfaces reduce heat exchangeand here is the need to avoid precipitation. The most comprehensive method is the removal of dissolved salts before heating ie the demineralization.
The demineralization of water can be achieved by various processes:
• chemical-physical (the so-called sodium-calcium treatment);
• by selective extraction of the ions constituting the salts using chemical compounds called selective ion-exchange resins;
Iron give water a yellow-reddish color and a metallic unpleasant taste, It can cause the formation of deposits with gradual occlusion of the tubing, and is often the cause of corrosion processes in plants.
In domestic use iron containing water dirty the bathroom fixture, the faucets and the linen.
The iron removal filters are equipped with active filtering masses capable of retaining the iron present in the water by its oxidation with sodium hypochlorite, making it fall in the form of flakes easily filterable.
The iron accumulated in the masses is periodically discharged with a countercurrent washing of the masses, carried out with sodium chloride, to restore the original capacity.
The filter is made up with a pressure tank with an automatic head with a timer to program the frequency of washes from onece a day to once a week.
It is advisable to install, upstream and downstream, a filter with washable cartridge not less than 50 microns to avoid the escape of unretained flakes
In presence of iron in larger amounts or for installations requiring continuous flow or with higher flow rates must be employed industrial iron removal filters manufactured in carbon steel, with hydraulic unit equipped with automatic timer to program the frequency of upstream washes.
These filters have filtering masses of the permanent type multilayer identical to those of the filters clarifiers, and to hold the iron they need for a prior oxidation of iron that can be obtained by adding to water a product oxidizing agent as chlorine or potassium permanganate, with a system of automatic dosing proportional to the flow of the water supplied
The denitrification of wastewater is a process of removal of nitrogen compounds present in solution in the form of NO3-(and in part of the NO2-) by facultative heterotrophic bacteria which, if placed in anoxic conditions (that is in absence of dissolved oxygen), are able to oxidize the organic carbonaceous substrate, using the oxygen bound to the nitrate NO3-instead of free oxygen O2, and releasing nitrogen gas as catabolite.
The denitrification process must take place under strictly anoxic conditions, at least in the microenvironment surrounding the bacteria. Unlike the nitrifying bacteria that are mainly represented by only two strains of bacteria, the denitrifying are of different types: Pseudomonas, Micrococcus, Archromobacter, Bacillus, Alcaligens; these types of bacteria are able to implement a complete conversion of NO3-to N2 (reaction intermediates are nitrite NO2-).
Denitrification, along with nitrification, allows to obtain good yields of total removal of nitrogen compounds (nitrogen and phosphorus are nutrients that, in excessive amounts, can cause oxygen deficiency in the surface water bodies, leading to the so-called eutrophication).
The plant section in which the process usually takes place is a square shape tank divided in two equal parts, communicating with each other only superficially, which allow you to give continuity to the treatment even if there is a need to drain a tank for maintenance. The basin is anoxic, so free from dissolved oxygen and aeration, receives the flow of sewage nitrified.
Biological purification of wastewater
Agriculture and forestry are the main activities responsible for the release of ammonia (NH3), they derives about 70% of the total emissions of these pollutants. Ammonia emissions from agriculture contribute in a decisive manner, through phenomena such as acidification, eutrophication and nitrogen runoff, pollution and excessive scale of sensitive environments.