Biological treatment plants of domestic wastewater for private houses

Purpose

NV type aerobic plants are most often used for treatment of domestic wastewater for private houses. Equipment is installed, where there is no possibility of connection to centralised sewage networks.

NV type biological treatment plants of domestic wastewater are intended for treatment of domestic or similar wastewater from the kitchen, bathroom, toilet and other similar-purpose facilities. Substances that cannot enter the treatment plant are as follows:

  • surface wastewater (off the roof, from the yard, etc.);
  • wastewater from a garage and other non-domestic – purpose facilities;
  • water from a basin or other receptacles that are larger than 1m3;
  • chemical substances, entering into sewage system of which is not provided according to their usage (oil products, agrochemical substances, etc.);
  • water after regeneration of filters of softening/removal of iron;
  • chemicals used at home (washing means, bleaches, softeners, degreasers) shall be use as provided in manufacturer’s recommendations.

Equipment advantages:


▪ factory enclosed biological treatment unit for domestic waste; 
▪ various capacities; 
▪ high level of treatment, removed 95–98% of pollutants; 
▪ no internal movable parts to be supervised or replaced; 
▪ serviceable, light-weight glass-fibre structure (easy transportation); 
▪ quiet operation and no offensive odour diffusion; 
▪ treated discharged water – transparent and odourless; 
▪ minimum power consumption; 
▪ no need in auxiliary filtering equipment; 
▪ easy maintenance and process automation; 
▪ easy installation.

Treatment plant is used as an underground facility. Supplementary collection (riser rings) depends on manifold deepening. Subject to the selected place, treatment plant may be installed in a green lawn or under the roadway (not recommended due to uncomfortable maintenance).

NV type wastewater treatment plants are of three modifications:
1.    NV-A type treatment plant of domestic wastewater: excess sludge is pumped off by  the assenisation machine
2.    NV-M type treatment plant of domestic wastewater: excess sludge is pumped off into bags of dewatered sludge
3.    NV-T type treatment plant of domestic wastewater: excess sludge is pumped off into sludge separator.

 

About the product

NV-A type biological wastewater treatment plant

NV 1÷4a type wastewater treatment plant consists of two chambers present in one tank (Figure 1). At first, wastewater, flowing into the plant, enters into the internal chamber, where it is mixed with the activated sludge with the help of air. Compressed air is necessary for supporting life of activated sludge and internal recirculation of treated wastewater. Air is provided with the help of the compressor (airblower). Biological treatment, i.e. treatment with activated sludge, is based on microorganisms’ activities. Purpose of the process is to bind soluble, colloidal and biogenic substances from wastewater into active sludge and separate activated sludge. Flake forming microorganisms multiply and form groups that cause adherence of protozoots and other bacteria. Microorganisms metabolyse (“eat up” and decompose) and destroy organic substances. Decomposition of organic materials and formation of the activated sludge takes place in the aeration section. Mixture of the activated sludge from the aeration chamber enters the external chamber (the secondary settling vessel), where, due to gravity forces, the activated sludge separates and falls down into the bottom part of the plant and the separated treated water lifts up and drains away. If the mass of microorganisms increases, the amount of the activated sludge also increases. Excess sludge is removed by the assenisation machine by pumping-off two-thirds of the plant capacity.

NV 1÷4a type biological treatment plant

Main structural parts:

1. Body (glass-fibre) 
2. Lid 
3. Bioload 
4. Aerator 
5. Inflow pipe 
6. Outflow pipe 
7. Air feeding pipe 
8. Airblower 

Supplementary collection

9. Riser ring 
10. Windblower housing

Installation site preparation

  1. Installation of the unit and its performance ensuring systems shall be performed in accordance with technical and/or working project. The designer is responsible for providing calculations, while preparing technical and working projects.
  2. The lid should be accessible for constant inspection and for proper functioning of the system.
  3. Check diameter of the sewage pipe. Do maintain a gradient that is required in order to ensure wastewater natural flow to the unit.
  4. PREPARATION FOR GROUND WORKS: clean a lager site than the treatment plant itself for at least half a metre around it.
  5. GROUND WORKS: ground works are carried out by strictly following STR 1.07.02:2005 regulation, technical and/or working project and the general construction norms for installation.
    In case, when, while ground digging works are performed, units or communications not indicated in the designed drawings are encountered, works shall be immediately stopped and the person performing technical supervision of construction or the authorised person shall be informed. Works in such an area can be continued only after receipt of the permission.
    Finishing ground works to the designed altitude, the foundation shall be check for weak or soaked soil, excavations, etc. Such soil shall be removed to the depth indicated by the person performing technical supervision of construction and shall be filled with a proper soil by compaction. The site shall be prepared to the altitude indicated in the project, soil shall compacted (compaction coefficient shall be from 0.95÷0.98, compaction layer shall be 200–300mm).

Installation of NV-A type treatment plant of biological wastewater

  1. Installation of wastewater treatment plant shall be performed following EN 976-2 standard.
  2. Treatment plant shall be installed according to the technical  and/or working project prepared in advance and harmonized with appropriate institutions.
  3. After evaluation of soil properties, an excavation shall follow overhaul dimensions of the plant. Stop digging till 20–30cm to the designed depth of the excavation.  Proceed with manual digging that is dig with the spade. This way the unit shall rest on a fixed soil by its bottom.
  4. Before lowering the plant to the excavation, IT IS NECESSARY TO CHECK, if the depth of the wastewater feeding pipe and the height of the treatment plant inflow coupling, and angles of the inflow and outflow pipes of the treatment plant do match.
  5. The unit shall be lowered to the excavation by using typical lifting mechanisms. After a careful lowering to the excavation, the unit shall be aligned with the help of the lever.
  6. For an appropriate performance of the treatment plant it is important for the overflow threshold at the top of it t be horizontal.  This is possible by firstly filling the round channel (inner lateral wall is the overflow threshold) at the top with water and by adjusting the position of the whole treatment plant with the help of a level, according to the position of this water surface, in respect of the overflow threshold. Temporary clogging outflow coupling is required for the water not to run-off, when filling the channel.
  7. Clearance between edges of the excavation and treatment facility are gradually filled with sand earlier delivered to the installation site that is poured by layers of 20–30cm, by thoroughly compacting with the help of mechanisms.   On presence of dry sand, it shall be irrigated during compaction.
  8. During installation (or in case of high level of ground water), when pouring sand into the excavation around the unit, the same unit shall be gradually filled with water. This is performed as follows: pour 20–30cm of sand into the excavation around the unit and simultaneously pour 20–30cm of water into the unit. Continue further by pouring 20–30cm of ground into the excavation around the unit and simultaneously pouring 20–30cm of water into the unit.
  9. Body of the facility shall be filled with sand to the inflow/outflow branch pipes that are then connected with inflow/outflow pipes.
  10. After filling the unit with sand to the upper part of the unit, cap it, in order to prevent the poured sand from entering into the inner part of the treatment plant, when continuing filling works.
  11. If unit has been deepened for more than 1.2m, additional rising ring (collected only on necessity) shall be applied. It is pulled without any fastening and sealed by using silicone.
  12. Finally, fill all the unit with soil to the designed altitude (recommended: if the unit is installed on the roadway: 50–70mm from the ground surface – if installed on the green lawn in the residential quarter: 200mm – if the unit is installed in an undeveloped territories (STR 2.07.01:2003, Section 450 )).

 

 

 

 

 

 

NV–M type biological wastewater treatment plant

NV 1÷4m type wastewater treatment plant of domestic wastewater consists of two chambers present in one tank (Figure 3). At first, wastewater, flowing into the plant, enters into the aeration chamber, where it is mixed with the activated sludge with the help of air. Compressed air is necessary for supporting life of activated sludge and internal recirculation of  treated wastewater. Air is provided with the help of the compressor (airblower). Wastewater is mixed with the activated sludge by the air, lifting through the aerator from the bottom to the top. Biological wastewater treatment is performed with the help of microorganism’s that decompose organic substances. 
Purpose of the process is to bind soluble, colloidal and biogenic substances from wastewater into activated sludge and separate active sludge. Flake forming microorganisms multiply and form groups that cause adherence of protozoots and other bacteria. Microorganisms metabolyse (“eat up” and decompose) and destroy organic substances. Decomposition of organic materials and formation of activated sludge takes place in the aeration section. Mixture of the activated sludge from the aeration chamber enters the external chamber (the secondary settling vessel), where, due to gravity forces, the activated sludge separates and falls down into the bottom part of the plant, from which, with the help of aeration system, once again rises into the aeration section - aerotank. Clarified wastewater enters into the collection duct, installed in the perimeter of the whole secondary settling vessel, and by passing through the flow regulator is removed through the outflow pipe. 
If the mass of microorganisms increases, the amount of the activated sludge also increases. With the help of the airlift, excess sludge is removed into the bag of dewatered sludge, fitted in the upper part of the plant. When the amount of the excess sludge in the bag is about 2/3 of its capacity, then the sludge is removed. Working cycle of the airlift is adjusted with the help of the airblower. By removing the sludge, air supply is stopped for 30 minutes for the sludge to settle at the bottom part of the plant.  With the help of the airlift, the settled particles of the sludge are removed into the bag of dewatered sludge, fitted in the upper part of the plant. A more precise working cycle of the airblower is set during the commissioning operations.

NV 1÷4m type biological treatment plant with bags of dewatered sludge

Main structural parts:

1. Body (glass-fibre) 
2. Lid 
3. Bioload 
4. Aerator 
5. Inflow pipe 
6. Outflow pipe 
7. Air feeding pipe 
8. Airblower 
9. Airlift 
10. Bag of dewatered sluddge 

Supplementary collection

11. Riser ring 
12. Windblower housing



NV-T type biological wastewater treatment plant


Domestic wastewater treatment system consists of two separate tanks – the NV type biological treatment plant and the sludge thickening device (Figure 1).       
NV 1÷4t type wastewater treatment plant of domestic wastewater consists of two chambers present in one tank (Figure 1; I). At first, wastewater, flowing into the plant, enters into the aeration chamber (Figure 1; 1, 2 positions), where it is mixed with the activated sludge with the help of air. Compressed air is necessary for supporting life of activated sludge and internal recirculation of  treated wastewater. Air is provided with the help of the compressor (airblower) (Figure 1; 12 position). Wastewater is mixed with the activated sludge by the air, lifting through the aerator (Figure 1; I, 4 position) from the bottom to the top. Biological wastewater treatment is performed with the help of microorganism’s that decompose organic substances. 
Purpose of the process is to bind soluble, colloidal and biogenic substances from wastewater into the activated sludge and separate activated sludge. Flake forming microorganisms multiply and form groups that cause adherence of protozoots and other bacteria. Microorganisms metabolyse (“eat up” and decompose) and destroy organic substances. Decomposition of organic materials and formation of activated sludge performs in the aeration section. Mixture of the activated sludge from the aeration chamber enters the external chamber (the secondary settling vessel) (Figure 1; I, 5 position), where, due to gravity forces, the activated sludge separates and falls down into the bottom part of the plant, from which, with the help of aeration system, once again rises into the aeration section - aerotank. Clarified wastewater enters into the collection duct, installed in the perimeter of the whole secondary settling vessel, and by passing through the flow regulator (Figure 1; I, 7 position), is removed through the outflow pipe. 
If the mass of microorganisms increases, the amount of the activated sludge also increases. With the help of the airlift, excess sludge is periodically removed to the sludge thickening device (Figure 1, II). Sludge thickening device consists of two chambers – chambers of excess sludge and collection of clarified water. Particles of sludge settle at the bottom of the tank and the clarified water enters into the chamber of collection of clarified water through the overflow duct. Water is returned to the treatment plant from the collection chamber through a T-joint fitted on the inflow pipe.  Excess sludge that dewatered  per se is periodically removed from the thickening device by pumping-off.

 

System of NV 1÷4t  type treatment plants of domestic wastewater with a separate sludge thickening device

Main structural parts:

I. Biological treatment plant 
II. Sludge thickening device 

1. Chamber of collection of clarified water 
2. Aeration chamber 
3. Bioload 
4. Aerator 
5. Secondary settling vessel 
6. Outflow pipe 
7. Outflowing water flow regulator 
8. Airlift 
9. Sludge chamber 
10. Lid 
11. Lid 
12. Windblower


Start-up and adjustment works

  1. Wastewater treatment plant commissioning works are commenced, when units are recognised as suitable to use and the permission to discharge wastewater into the environment is issued in the valid order (Wastewater treatment regulation No. D1-412 as of 11 September, 2006).
  2. Duration of commissioning works of units is 3 months from the date of recognizing the unit suitable to use, when air temperature is no less than +10 0C during day-time, and does not fall below 0 0C during night-time.
  3. Conformity of actual wastewater amounts and contamination to the designed ones shall be checked.
  4. Aeration system shall be tested in the unit.
  5. The unit shall be poured with sludge infection by delivering activated sludge or by filling the unit with live (stream, pond) water and growing activated sludge.
  6. When sludge concentration in the unit reaches ≥ 20%, samples shall be obtained from the outflowing and cleaned water, in order to determine quality.
  7. Person supervising the units shall be familiarised with the main service rules of the unit.
  8. Commissioning report shall be drawn.
  9. During commissioning works the  level of up to 50% of treatment of the inflowing primary wastewater contamination according to BDS5 is reached. In this case, during commissioning works, in presence of maximum primary wastewater contamination up to 330mg/l, contamination of cleaned wastewater according BDS5 may reach up to 165mg/l.