HNV type biological treatment plants of domestic wastewater for settlements and newly built quarters

Purpose

HNV type domestic wastewater treatment plants for settlements and newly built quarters 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 recommendations.

Fig. 1. Technological scheme of biological treatment plants of domestic wastewater for settlements

1. Manual grating 
2. Sand trap 
3. Flow collection/distribution well 
4. HNV type wastewater treatment plant 
5. Sludge thickener 
6. Debit measurement well 
7. Airblower

Equipment advantages:

  • various capacities;
  • high level of treatment (removed up to 98% of pollutants);
  • no internal movable parts to be supervised or replaced;
  • serviceable, light-weight glass-fibre structure (easy transportation);
  • small-size enclosed type products;
  • quiet operation and no offensive odour diffusion;
  • treated discharged water – transparent and odourless;
  • minimum power consumption;
  • easy maintenance and process automation;
  • installation is possible both, under the ground (in case of interference with underground structures) and in a special filling above the ground.

 

 

HNV type wastewater treatment plants are of two modifications:

  • I modification (HNV-P): primary settling tank, aerobic reactor, secondary settling tank;
  • II modification (HNV-N): anoxious chamber, aerotank of prolonged aeration, secondary 
    settling tank.

 

About the product


HNV-P type treatment plants



The plant of HNV-P modification is constructed from a primary settling vessel, an aerobic reactor, a secondary settling vessel (with a module of thin wall) in one tank. Usually, grating (or a pump crusher) and a sand trap are installed before the plant of HNV-P modification. 
The fed wastewater enters the primary settling vessel. Wastewater is treated for 2 hours in the primary settling vessel. The sludge settled in the settling vessel with the help of the air pump is constantly removed into a separately fitted sludge stabiliser. After the settling vessel, sludge enters the aerobic reactor with the bioload. Biological treatment, i.e. treatment with activated sludge, is based on microorganisms’ activities. Wastewater, requiring treatment, is aerated. Flake forming bacteria (microorganisms) multiply and form groups that cause adherence of protozoots and other bacteria. Microorganisms metabolyse (“eat up” and decompose) and biologically destroy organic substances. Constant feeding of oxygen is required. Purpose of the process is to bind soluble, colloidal and biogenic substances from wastewater into activated sludge and separate activated sludge. Basically, the process of activated sludge is a live system, thus appropriate actions are required. In order to maintain certain necessary microorganisms, appropriate “feeding, growing, multiplication” is required. Sudden changes in working conditions may result in a shock. Thus, the bioload, to which attach microorganisms that cannot be removed by uneven wastewater flows. Excess sludge from the aerobic reactor is removed into the primary settling vessel with the help of the air pump. After the aerobic reactor, the mixture of wastewater and sludge enters the secondary settling vessel with the thin-walled module, from which the settled sludge is returned into the aerobic reactor with the help of the air pump, and the cleared wastewater drains away from the facility.


Technological schemes of HNV-P type wastewater treatment plants

I option. HNV-P type wastewater treatment plants amounts from 5m³/p to 24m³/p (in one body)




 

II option. HNV-P type wastewater treatment plants amounts from 25m³/p to 55m³/p (the secondary settling tank in a separate body)



Treatment efficiency of HNV-P type wastewater treatment plants


 

HNV-N type treatment plants


 

 

The plant of HNV-N modification constructs from an anoxious chamber, an aerotank of prolonged aeration and a secondary settling vessel in one tank. It is necessary to install a grating (a pump crusher), a sand trap, a septic tank and, on necessity, a grease trap against the plant of HNV-N modification. 
Anoxious aerobic treatment conditions (oxygen from nitrates is used for biological processes), that is inlet wastewater is mixed with the mixture of nitrified sludge, which is fed from the aeration chamber. Nitrate nitrogen is removed from sludge in the anoxious chamber and settlement of sludge is improved (sludge index and danger of denitrification in the secondary settling vessel decrease). After the anoxious chamber wastewater enters the chamber of prolonged aeration (the aeration reactor), where wastewater is aerated and then aerobic wastewater treatment is performed and excess nitrogen oxidizes into nitrates. The mixture of wastewater and sludge from the aerotank enters the secondary settling vessel, where the separated activated sludge returns to the anoxious section, and cleared wastewater discharges from the facility. Excess activated sludge is periodically removed from the facility, when its concentration reaches the maximum permissible concentration in the aerotank. 
The highest wastewater treatment efficiency in achieved in plants of HNV-N modification; they are also easy to service; no green sludge formation, no anaerobic processes take place during wastewater treatment, thus there is no offensive odour diffusion, fully stabilised sludge is removed, due to very low loads of sludge sustained, amounts of excess sludge are lower than of facilities of other modifications.

Technological schemes of HNV-N type wastewater treatment plants

I option. HNV-N type wastewater treatment plants amounts from 5m³/p to 24m³/p (in one body)

II option. HNV-N type wastewater treatment plants amounts from 25m³/p to 55m³/p (the secondary settling tank is in a separate body)


 

Installation

 

Installation of the unit and its performance ensuring systems shall be performed in accordance with the technical and/or working project.

Installation site preparation
We recommend the following:

  1. installation site for the facility shall be selected so that it would not be flooded by surface waters;
  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 larger site than the treatment plant itself at least half a metre around it;
  5. GROUND WORKS: ground works are carried out by strictly following the STR 1.07.02:2005 regulation, the 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 Schemes are encountered, works shall be immediately stopped. The person performing technical supervision of the construction or the authorised person shall be informed and the works shall be continued only on receipt of the permission. 
    Finishing ground works to the designed altitude, the foundation shall be checked for weak or soaked soil, excavations, etc. Such soil shall be removed to the depth indicated by the person performing technical supervision of the construction and shall be filled with proper soil by compacting. The site shall be prepared to the altitude indicated in the project, soil shall be compacted (compaction coefficient shall be from 0.95÷0.98, compaction layer shall be 200–300mm).

Installation of the facility

Treatment plant shall be installed according to the project prepared in advance and harmonized with appropriate institutions. 

ATTENTION: unit installation requires a special attention, as further performance depends on it. 
We recommend the following:

  1. installation of wastewater treatment plant shall be performed following the EN 976-2 standard;
  2. 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 fixed soil by its bottom;
  3. before lowering the plant to the excavation,IT IS NECESSARY TO CHECK, if diameters of couplings match diameters of the wastewater inlet pipe and the treated water outlet pipe; also check, if the depth of wastewater feeding pipe and the height of the treatment plant inlet coupling, and angles of the inlet and outlet pipes of the treatment plant do match;
  4. 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 by the help of the lever;
  5. clearance between edges of the excavation and treatment facility shall be gradually filled with sand earlier delivered to the installation site that is poured by layers of 20–30cm, by thoroughly compacting.On presence of dry sand, it shall be irrigated during compaction;
  6. 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;
  7. 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 digging works;
  8. pour sand to the limit for the lid of the treatment plant to be in the same level as street or pavement coating, if the plant is installed on the roadway: 50–70mm from the ground surface – if installed on the green lawn in the residential quarter: 200mm – if the plant is installed in undeveloped territories (STR 2.07.01:2003, Section 450));
  9. when installing the treatment facility under the roadway, a slab of reinforced concrete of 200mm thickness is fitted, distributing the transport load off the treatment facilities;
  10. in case of high level of ground water, the unit shall be anchored to the concrete block by a stainless steel belt.
  11. Check, if the necessary airblower model, described in the description of the treatment plant, is in the set.
  12. Airblower can be installed in a utility room, though no more than at a distance of 15m off the treatment plant, in order to ensure feeding of the required amount of oxygen and to avoid loss of air flow pressure. The room shall be ventilated and fitted with electricity. On necessity, the airblower may be also mounted outside. Then it is mounted in a special box of glass-fibre, protecting it against rain and dust.
  13. Mounting the airblower outside, the box cannot be placed in the place, where water is likely to flow-in and accumulate.
  14. Mounting the airblower in a room, place it so that it would not contact wall or any other support.
  15. Installing the air feeding pipe, it is important to prepare of it this much to bypass sharp angles or places, where it would be affected by a too high load with a reserve. It is required to minimize the number of pipe elbows that air would flow with a smooth gradient to the side of the unit, in order to avoid loss of air flow pressure.
  16. Air feeding pipe shall be laid on a harder foundation, for example, on an untouched soil surface in a channel. Fill it with ground carefully, in order to avoid damages.