Domestic wastewater treatment plant

1,Project situation

   This raw sewage source of sewage treatment plants is domestic sewage, it will be pollute the near surrounding before treatment, so it must be treated before discharge, to make the treated water reused.

According to actual condition, aiming to such project, treatment process adopt Anaerobic- Oxic , advanced technics , better treatment effect, after treatment, the outlet water can reach sewage integrated discharge standard(GB8978-1996)1 grade discharge standard and reused in washing toilet.

2,Design base

1,Municipal area environment noise standard(GB3096-93);

2,Outdoor drainage design norm(GBJ14-87);

3,Water supply drainage project structure design nor(GBJ69-84);

4,sewage integrated discharge standar(GB8978-1996).

3,Design principles

1,Fully considering secondary pollution, equipment require low noise, no obvious peculiar smell, treatment facility should have seal measure, reduce the influence to surroundings;

2,Simple system operation, convenient to maintenance and management;

3,Treatment system can automatic operate, low operate cost , save investment;

4,Few sludge yield, and guarantee sludge has reliable outlet;

5,Treatment measure has bigger adaptability,emergency ,which can meet up water quality and volume variety;

4,Design Parameter

1,Sewage properties

2,Sewage water volume:25m³/d

3,Inlet outlet water quality:

Inlet water is domestic sewage;

Outlet water required: Reach to first grade sewage integrated discharge standard(GB8978-1996) ( referring to similar practice)

5,Design Scope

The scope of sewage treatment plants : sewage treatment structures and matched structures technics, civil engineering, electric,meter and power supply line and inlet outlet water pipeline design etc.        

6,Process choose

1,Sewage characteristic

Water quality content low and steady, better degradability, belong to low concentration sewage

2,Process confirm

Traditional sewage treatment process can divide into biological membrane manner and activated sludge manner, biological membrane suitable to small water volume,steady water quality ,low concentration sewage water quality, better system commission. Steady back operation, better operability. Sewage water quality set as traditional routine: COD_Cr ≤300mg/l,BOD₅ ≤200mg/l,

Combine our company past success practice, suggest sue biofilm manner treatment process, plan to adopt A/O biological contact oxygen process as main treatment manner.

This project with high organic ingredients, BOD5/CODcr=0.6 , better biodegradability , due to ammonia nitrogen and organism content is high, especially organic nitrogen, when biological degradation organism, the organic nitrogen will be express in the form of ammonia nitrogen, ammonia nitrogen is a key pollution control index, so such sewage treatment adopt anoxia oxic A/O biological contact oxidation process, so the biochemical tank divide into A grade anoxic tank and O grade oxic tank two parts.

3. Treatment process:

     Sewage---- bar screen-----septic tank--- equalize tank-----A grade anoxic tank----- O grade oxic tank ------ settling tank----sand filtering tank---cleaning water tank---- reuse

               UV-sterilizer

The domestic sewage first pass by bar screen net to remove bigger suspended solids, then enter into septic tank and equalize tank to make pretreatment , due to sewage flow rate is different in peak time, equalize tank main function is balance water quality and volume, after that, sewage willl lift to package sewage treatment plant, first pump in to A grade anoxic tank, to go ahead biological treatment. In A grade anoxic tank , due to the sewage organism content is high, microorganism in anaerobic condition, now the microorganism is facultative , they will transform the organic nitrogen intoammonia nitrogen, at the same time, using organic carbon source as electron donor, to make the NO₂-N,NO₃-N translate into N_2, and using part of carbon source and ammonia nitrogen synthesis new cellular material. so A grade tank with certain function of organic matter removal , relieve the organic load of follow-up O grade biochemical tank, to benefit to nitrification, and rely on high concentration organism in sewage , to finish denitrification, finally eliminate the nitrogen eutrophication pollution. By A grade tank biochemical action, the sewage still some organism and higher ammonia nitrogen, in order to make organism further aerobic degradation, at the same time, when carbonification tend to finish, nitrification can smoothly going on , thus set O grade oxic tank.

The outlet water from A grade tank will flow into O grade tank, the O grade biochemical treatment rely on autotrophic bacteria finish, they utilize organism resolve generate inorganic carbon or carbon dioxide in air as nutrients source, to make the ammonia nitrogen translate into NO₂-N,NO₃-N. a part of O grade outlet water enter into settling tank to sediment, another part backflow to A grade to proceed A grade tank to proceed internal recycle, to realize nitrifying purpose. All equip with biological padding in A grade and O grade biochemical tank, the whole biochemical treatment process all rely on many kinds of microorganism to finish.

The dissolved oxygen is control about 0.5mg/l in A grade tank, above 2.0mg/l in O grade tank, air water ratio 12:1; part of outlet water in O grade tank backflow to A grade tank, reflux ratio is 200%; part of sewage flow into settling tank, to make solid liquid separation; the effluent water enter into sand filtering tank to make further purify treatment, then enter into cleaning water tank, it will be reuse for irrigation, washing tiolet etc after disinfection.

Little sludge from settling tank will pump into sludge tank, mud will transport outside after dry.

7,Process Description

1,Bar screen   1 pc

Main used in intercept big block floater in sewage, to guarantee follow-up processing structures normal operation and effective reduce load, supply guarantee for system long term normal operation, grid bar gap is 5mm, size:500*300mm.

2, Equalize tank

Size: 8m³ , design water retention time 8h.

Due to each time water quality,volume is different, the peak flow rate of average flow rate 2~8 times, thus sewage treatment system steady operation, equalize water volume and homogenize water quality, build-in sewage pump and backflow measure, equip with aeration system to proceed pre-aeration, to guarantee certain rated flow rate lifting to integrated sewage treatment equipments and follow-up treatment steady, lifting pump chose 2pcs QW type sewage pump.

3. Package sewage treatment plants

This technical process adopt integrated sewage treatment plants, such plants mainly aiming at domestic sewage and industrial organic sewage, mainly adopt the mature bio-chemical treatment contact oxidation manner, total composed of the following 6 parts:

(1)A grade biochemical tank

 In order to control the dissolved oxygen in A grade biochemical tank about 0.5mg/l, adopting interval aeration. The padding in A grade biochemical tank adopting new type elastic padding, height is 2.0m. such padding with the advantage of no easy blocking,light weight,big specific surface area, treatment effect steady etc, easy to maintenance and change , retention time 3.5hours.

(2)O grade biochemical tank

The O grade biochemical tank equip with columnar biology carrier padding, this padding specific surface area is big, is 16-20 times comparing with common biological padding, keep higher biomass, to reach the purpose of removing organic pollutant, aeration device adopting air blower and micropore aerator, the oxygen utilization rate is above 30, effective save operation cost. Retention time 7 hours, air water ratio about 12:1.

 (3)Settling tank

   The sewage still contain large number of suspended solid after treated by O grade biochemical, in order to make the effluent water SS meet up discharge standard, adopting vertical settling tank to make solid liquid separation, 1 set , surface load 1.0m³/m²·hr. the settling tank sludge adopt air lifting device lift to sludge tank, at the same time, according to actual condition to make part of sludge lifting to A grade biochemical tank to proceed sludge backflow, increase the sludge concentration in O grade, improve removal efficiency.

(4)Cleaning disinfection tank

Using UV sterilizer, After biochemical,sediment , then make disinfection treatment.

(5)Sludge tank

The supernate backflow to contact oxic tank to further treatment, few sludge after digestion. clearing manner can sucking and transport out from sludge tank bottom using dung-cart.

(6)Air blower room

Air blower set in the air blower room, equip with silencer.

,Biology carrier padding

    Main characteristic as following:

(1),using superior polyene type heat resistance and corrosion resistance to aging polyamide high quality as material , mix with hydrophile,adsorption,heat resistance etc auxiliaries, long time soak in sewage won’t degradation, won’t produce harmful effluence to organism.

(2) Adopting special wiredrawing, sliver fur process, to make suspended type three-dimensional elastic padding, the padding can fully uniform stretch in effective area, make water,air ,biological membrane fully contact exchange, biological membrane not only spread each wire, keep better biological activity and interspace variability, can get bigger and bigger specific area in operation process, and can proceed better metabolism.

 (3),High specific surface, single side specific surface of living beings carrier padding can reach 320 m2/m3, two sides can reach 640m2/m3, biomass in unit volume is high, can reach the purpose of reduce hydraulic retention time.

(4)Microbial High-activity , the microorganism membrane grow in padding surface stay in high activated increased logarithmic phase due to padding fluidify collision ,aeration scour , with high removal rate.

(5),Suspended padding, exchange convenient, service life above 10 years.

(6),inside the padding grow anaerobic bacteria, which can generate denitrification effect and denitrification; external grow oxic bacteria , to make resolve organism. So synchronism exist nitration and denitrification function.

,Micropore aerator

(1),long service life, convenient maintenance, uniform aeration.

(2),install convenient, small buoyancy and vibration, no need special fixed.

(3),Oxygen transform efficiency, small bubble, around micropore uniform air leaving, small pressure damage.

8,Main structures,equipments design parameter

  1,bar screen

specification:500×300mm

material: stainless steel

mesh:5x5mm

quantity:1pc

2,Equalize tank

Retention time:8h

Effective volume:8m3³

Material: Reinforced concrete

Quantity:1pc

3,Sewage lifting pump

Model: WQ5-10-0.75

Flow rate:5m³/h

Head:10m

Power:0.75kW

Quantity:2pcs

4,Integrated sewage treatment plants

Specification:5500×2000×2000mm

Material:A3 Carbon steel antiseptic

Quantity:1pc

5,Air blower

Model:HC-40IS

Air volume:1.09m³/min

Air pressure:0.3kgf/cm²

Power:1.0kW

Quantity:2pcs

9,Main equipments list (25KLD package sewage treatment plant)

10, Mechanical and electrical energy consumption flow

                                 unit:kw

11,Microcomputer control operate design

This sewage treatment system control adopt PLC as central control unit, mainly control the sewage lifting pump,air blower mutual changing-over.

1,sewage lifting pump

Adopting WQ type lifting pump, with strong discharge mud ability,no blocking, can effective pass 10mm solid particle. 2pcs lifting pump, 1 pc in operation, another pump stand by, pump start is controlled by equalize tank floater , float switch is composed of fully sealed glass structure mercury, external foam plastic as carrier , the floater divide 3pcs according to equalize tank liquid level.

2,Air blower

Model: HC-40IS, with small noise, long service life, system process adopt air blower to make aeration within 24h exchange use, when sewage pump in equalize tank stop, air blower aeration 0.5h internal two hours, each air blower automatic changeover each operate 24hours, this is controlled by control cabiet

3,Whole system work process:

1),when sewage liquid level in equalize tank below lifting pump, the aeration air blower keep operate 10 minutes each half hour , pump can’t start.

2),when the liquid level below start pump water level, above stop pump water level, manual start water pump1 and water pump2, air blower can operate in continuous alternately operation.

3),when liquid level in equalize tank below alarm water level, 2pcs air blower in alternate working, water pump operate without stop, stop it till sewage liquid level reduce to below stop pump water level.

Due to control system has above function and characteristic, which made the integrated sewage treatment plants fully control operation within 24hours, it can save labor and energy, and guarantee the outlet water reach to design standard.