Potable Water Production
Briefly about Water Intake I
The central complex for providing potable water for the city of Subotica is Water Intake 1, since from there, depending on the season, 75-85% of the required water quantity is supplied.
Water Intake 1 is located on the northern boundaries of the city, in the neighbourhood of the Zorka factory, and is equipped with 29 active wells having, currently, a total capacity of ~ 350 l/sec.
The wells are drilled to about 200 meter depth and cover 2-4 aquifers.
The first aquifer is at about 100-120 m depth. The aquifers are divided by impermeable layers of clay so the contamination of water through surface soil layers is impossible. In case some works have been done on the wells of the PUC (replacements of submersible pump, regeneration...), before these are put into operation again, disinfection, flush and the sampling of the well water are made. The wells are put into operation only when the lab results show that the well water meets sanitary requirements bacteriologically and chemically.
Each well is equipped with an adequate submersible pump and the required measuring and controlling equipment.
Depending on the needs of the city, only a certain number of wells operate at a time. The submersible pumps pump the water from the well to the collection pipeline by which the water is transported to the sand separator, where the possible sand content is separated from the potable, still raw and untreated water.
Leaving the separator, the water enters the so called “filter station”, i.e. the water treatment installation consisting of 4 filtering lines.
Each filtering line can treat maximum 100 l/sec., thus the capacity of the whole water treatment installation is 400 l/sec. maximum.
Prior to the filtering line, some elements are added to the water, which improve the separation of undesirable matters (arsenic, ammonia and iron) making disinfection at the same time.
This treated water is further transported to the tank for treated water having 3000m3, which serves to compensate the imbalances in daily consumption and also as a reserve for cases, when consumption exceeds production capacities.
The treated water leaves the tank and in free-fall it enters the high pressure pump station and from there the water is transported to the city by one of the 6 pump units selected in accordance with the consumption needs.
An automatic disinfectant dosing system has been installed on the outlet pipeline to the city, VZ 1, which maintains concentration set by the law.
Simplified Chart of the Potable Water Treatment Process – Water Intake I
Treatment of Water for Drinking
The quality of the underground water we draw is very good both in chemical and in bacteriological view. Since this water is found under several layers of clay, it is very well protected from external contamination, and practically, its content has not been changed over the times.
In relation to the current Regulations on the Sanitary Compliance of Potable Water, our so called raw water contains excess salts of iron, arsenic and ammonia. Owing to this fact, we started a research work in 1980s as a preliminary action to the implementation of raw water treatment in Subotica. The above indicated components in the water are present in diluted form of their salts.
Iron is a natural component of underground waters. Its quantities in our water generate technical problems in the distribution of the water through the pipelines. Namely, iron compounds turn into sediments in the pipes, which cause plugging, and when it appears on the taps of consumers it causes aesthetical disturbance during consumption.
Ammonia is also a natural component of deep layer waters. Its content is limited because of the consequences it causes in the supply network, because in the presence of oxygen and micro-organisms a process goes on resulting in a sanitary incompliance of the water.
Arsenic in its compounds are present everywhere on the Earth’s shell. It is less presented in rocks than in layers of clay. It enters water through dilution or soil eroding or as a result of erosion processes.
The arsenic present in our water is of natural, geological origin, which is harmful in large quantities; therefore its content is limited.
The above indicated salts are eliminated from the water through oxidation and filtration in the “Water Factory” thus after such treatment they satisfy the requirements of the Regulation for the Sanitary Compliance of Potable Water.