Screening: showing is clears big solid objects from sewerage, such as refuse, rocks, can, fabric garbages, plastic bags, subdivisions, etc. , in order to avoid obstruct pumps, valves and piping and harm other subsequent processing equipment. Coarse sieve trough spacing is 50mm-100mm. Furthermore, testing spacing of all right showing is 10mm, 6mm or 2.5mm etc. The all right spacing can be more efficient, but it will besides faster to be debris clogging.
Grit remotion: To forestall grit damaged on the operation of machinery and equipment, cut down precipitation in the grapevine and prevent accretion at sludge digestion armored combat vehicle. The entryway of grit trap normally have adjustable angle of recreation home base to command the influx of the sewerage. The grit can be hasty to the underside, and so the grit take arm will jab the grit to bottom side of the trap. The clasp is removed by clasp classifier.
Primary deposit: About 50-70 % of the solids and particulate affairs of size larger than 0.1 millimeter settle down under influence of gravitation. A decrease between 30-40 % in the figure of coli signifiers is obtained. The sludge and is removed by automatically operated devices without upseting the operation in the armored combat vehicle. To accomplish a peculiar grade of solids removal the clip of detainment of a package of sewerage must be such that all atoms below a certain size can fall to the underside of the armored combat vehicle after come ining at top H2O degree.
The flight of the atom is shown in the simplified diagram above.
- Time of detainment = dbl/Q=d/Vs
- Which simplifies to: VS =Q/A bl = country, A
- Therefore VS = Q/A
Simultaneously a little sum of biological action besides takes topographic point in which microbes nowadays in the sludge onslaught complex organic solids and interrupt them down to simpler soluble substances and ammonium hydroxide. The lubricating oil rises to the surface to organize a trash which is removed by scum aggregator. Purpose of deposit is to take suspended solids and cut down the strength of the sewerage. Deposit is the subsiding and remotion of suspended drosss which occur when H2O stands still or flows easy through a basin or armored combat vehicle. There is negligible turbulency and hence atoms of high denseness tend to settle down and organize a sludge bed at the underside of the armored combat vehicle whereas clarified H2O will be collected through the mercantile establishment.
Biological Treatment:
Activated sludge procedure is the most common option in secondary intervention and is besides a method of suspended cell sewerage intervention method. It starts with aeration that encourages the growing of bugs in the waste. The bugs feed by the organic stuff, which so allows solids to settle out. Activated sludge is contain full of bacteriums and continually re-circulated back to the aeration basin to increase the rate of organic decomposition. In natural sewerage, bacteria predominate during the keeping clip in the aeration armored combat vehicle. The figure of suspended bacteriums lessening but those associated with floccules greatly increase in figure. During the keeping period, a part of dissolved organic substrate is mineralized. Another part is converted to microbic biomass. In the advanced phase of aeration, most of the microbic biomass is associated with floccules that can be removed from suspension by settling. The General design of aeration reaction clip of sewerage is about 6 hours to 8 hours. Temperature affects the reaction rate of microorganisms, each extra 10 & A ; acirc ; „? temperature can do the dual reaction rate. Furthermore, the common nutrient to micro-organism ratio is 0.1 & A ; egrave ; ‡?0.5kg BODi?A?d.kg MLSS
Concluding deposit: The oxidised sewerage from the aeration chamber is led into the concluding deposit armored combat vehicle where it is detained for 4 hours. The solids-liquid separation effected by gravitation to bring forth a clarified wastewater for discharge after biological intervention. The sludge that collects in the concluding deposit armored combat vehicle is called activated sludge. It differs from the sludge in the primary deposit armored combat vehicle in that it is practically unoffending and is rich in bacteriums, N and phosphates. Part of activated sludge is pumped back into the aeration armored combat vehicles i n the activated sludge procedure and the remainder is pumped into the sludge digestion armored combat vehicles for intervention and disposal. ( Microbiologyprocedure.com ) ( Yu Shu adult male )
Disinfection
There besides will hold bacteriums after concluding deposit, so it is need to disinfection to guarantee most of bacteriums a dead. The most common methods in Hong Kong is applied extremist violet disinfection system and add the Na hypochlorite solution before being discharged of wastewater.
From the above description, we can see that the typical secondary sewerage intervention works is rather big. For illustration the size of primary deposit armored combat vehicle, aeration armored combat vehicle and concluding deposit armored combat vehicle are over 2000m2 per armored combat vehicle at ShaTin sewerage intervention works. Even the entire size of one set of primary deposit armored combat vehicle, aeration armored combat vehicle and concluding deposit armored combat vehicle at Stanley is besides over than 1000 m2.So the typical activated sludge procedure is non suited for little area/ premises. So it can be use
The little intervention capacity sewerage intervention workss ( little capacity
STPs ) . The design flow rate is about 600 m3/d ( population equivalent of approximative 1500 ) is suited of premises in Hong Kong. The rating standards of the sewerage intervention engineerings for little scale STPs include: land usage, operation and care friendly, intervention efficiency, intervention flexibleness and potency for Hong Kong application.
Small graduated table STPs are common application in Hong Kong:
- Oxidation Ditch ( OD )
- Revolving Biological Contactor ( RBC )
- Sequencing Batch Reactor ( SBR )
- Membrane Biological Reactor ( MBR )
Oxidation Ditch ( OD )
The oxidization ditch is a kind of equipment used for a long-run aeration and is characterized by a long sludge age in the system. It consists of a long channel of an egg-shaped or round form equipped with a horizontally mounted rotor for bring forthing a H2O flow and rousing H2O in the channel to provide O for the biological procedure. ( RD 2035 ) Cyclotron oxidization armored combat vehicle consists of a ring composed of sewerage armored combat vehicle, 1 m to 1.5 m deepness. Sewage rotary velocity is 0.3 to 0.6 m/s
Thought it requires a comparatively big country, the oxidization ditch has a simple construction and can be easy operated every bit good as being able to take N. Therefore, it is used in comparatively little sewerage treating workss.
Advantages of utilizing the oxidization ditch are:
- Easily care.
- Robust to lade fluctuations and smaller sludge measure.
- Aeration efficiency can be easy controlled by altering the rotary motion velocity of the rotor and the dipping deepness.
- Little energy is required as the rotor is of high efficiency.
- Perform nitrification and denitrification in the procedure.
- Disadvantages of utilizing oxidization ditch are:
- It requires a big country because the armored combat vehicle is big and the deepness is shallow,
- It besides require for little deposit armored combat vehicle after oxidization ditch.
Revolving Biological Contactor ( RBC )
The Rotating Biological Contactor ( RBC ) is a unit consisting of a series of closely parallel phonograph record mounted on a rotating shaft which is supported merely above the surface of sewerage to be treated. The design of both Biomass thickness and velocity of rotary motion besides are cardinal. Aerobic debasement of the pollutants takes topographic point on the phonograph record surface which Micro-organisms grow on it. There are least 85 % removal rate of the biochemical O demand ( BOD ) from domestic sewerage should be designed in RBC procedure. ( LAM Ho Kai )
Advantages of utilizing the RBC engineering are:
- longer contact clip and higher degree of intervention
- Simpler operation than activated sludge.
- Less susceptibleness to upset from alterations in hydraulic or organic burden than the activated sludge procedure.
- Sewage from domestic and other biodegradable industrial discharges besides can be treated.
- Procedure can besides be designed to take ammonium hydroxide N.
Disadvantage of utilizing the RBC engineering is:
It besides require for little primary and concluding deposit armored combat vehicle after RBC engineering.
Though the size is much smaller than activated sludge procedure works and oxidization ditch, works of RBC is big.
Sequencing Batch Reactor ( SBR )
The sequencing batch reactor ( SBR ) is a fill-and-draw activated sludge intervention system. It includes a generic system of variable volume activated sludge in which aeration, deposit and decant are combined in a individual reactor. Therefore, there is no needed for secondary clarifier or return sludge installations. The operation of the SBR, it consists of five distinguishable periods ( Fill, React, Settle, Draw and Idle ) , which comprise one complete reactor rhythm.
- Fill: The natural sewerage fed to the reactor. In Fill period can be inactive, assorted or aerated.
- By pull stringsing the existent specific growing rates of the bugs and modulating the O tenseness in the reactor, the being choice can be controlled.
- React: Aeration and commixture is take topographic point at reactor.
- Settle: Microbes are separate by deposit during a period. This is quiescent settling and separation of MLSS from the treated sewerage
- Draw: This is procedure which backdown of treated sewerage from the reactor
- Idle: This is procedure which removes the sludge from the reactor underside.
- Advantages of utilizing the SBR procedure are:
- No secondary clarifier and return activated sludge pumping procedure are required.
- Footprint is little.
- High tolerance for extremum flows and daze burdens.
- Avert assorted spirits suspended solids washout during extremum flow events.
- Clarification under ideal quiescent conditions than typical activated sludge intervention system.
- Disadvantages of utilizing the SBR procedure are:
- Requirement of an equalisation armored combat vehicle.
- Requirement of procedure expertness in programming the rhythms.
- Care is more complicated cause by complex Automatic control system
- It is easy pulling the sludge when the extraction spirits procedure.
Membrane Biological Reactor ( MBR )
Membrane bioreactor ( MBR ) procedure is a alteration of the activated sludge procedure. The liquid-solids separation is carried out by extremely specialised membranes, as compared with the secondary colonist in the continuous- flow activated sludge procedure. Mixed spirits suspended solids ( MLSS ) degrees maintained in 8000 to12000 mg/L in bioreactors can be increase the intervention efficiency. The membrane can be act as a filter to take the pollutants from the sewerage in either suspended or dissolved. MBR is uniting the membrane engineering and activated sludge procedure for the intervention of sewerage, so it can be replacing for the concluding clarifiers. The membrane stuffs include polymeric stuffs or ceramics. These stuffs are porous and achieve solids and liquid separation automatically. The pore sizes of the membranes are normally from 0.03 to 0.4 micrometers. Supplying a most effectual pore size of less than 0.01 micrometers can be enhances the effectivity of this filtration public presentation. The pore size of membranes which less than 0.01 micrometers can be stops the virus, bacteriums.
The MBR procedure can be in two different constellations. The first constellation is a side-stream system, in which the membrane is independent of the bioreactor. The MLSS of the bioreactors is pumped around a recirculation cringle incorporating a membrane unit where the permeate is discharged and the retentate is returned to the bioreactor. The 2nd constellation is a submersed MBR, in which membrane faculties are immersed within the bioreactor. This is presently the most common MBR constellation for municipal applications. The MBR engineering is no primary or secondary colony phases required and no extra third intervention or UV phases to accomplish really high disinfection quality.
Advantages of utilizing the MBR procedure are:
- It has a high quality wastewater after intervention cause by removal rate of suspended solids is least above 0.1 micrometer.
- It has low energy ingestion cause by the system is working at sub-pressure lower than saloon up to 0.5 saloon
- It has high sludge concentration. The procedure enables working in high bio mass concentration. The concentration of sludge is 4 times higher than other procedures of biological of sewerage intervention.
- The procedure is without chemical ingestion. At Chemically Enhanced Primary Treatment and Secondary Treatment is required chemical for Enhance Settle and sludge thickener
- Its operation is simplified. The operating system is simple and dependable in footings of work force and care. The membrane has high resistant for oxidization.
- It requires little footmark. The biological dissolution, solid separation, outflowing shining and sludge thickener are besides taken topographic point in same armored combat vehicle.
- Disadvantages of utilizing the MBR procedure are:
- The initial cost of membranes is high.
- The entrance sewerage requires testing before come ining the membrane bioreactor armored combat vehicle.
- Chemical cleansing after operation for a period is required.
