- DESCRIPTION and FUNCTION:
(1st) Process - (Denitrification)
The wastewater flows through the screen basket to the contact zone - which is aerated by means of coarse bubble aeration. Rough impurities are pulverised by the stream of air and go through to the treatment process. For non-degradable particles it is necessary to remove and deposit with household waste.
(2nd) Process - (Activation-Nitrification)
The activated nitrification areas are fitted with a fine-bubble aeration system. A membrane blower supplies the air for aeration. The fine-bubble aeration elements are placed at the bottom of the activation tank. Here: organic pollution in the water is removed biologically with high concentrations of dissolved oxygen. The organic substances are oxidised to form carbon dioxide plus water whilst the organic carbon is partially used for the growth of the activated sludge biomass. Further, the ions of ammoniac nitrogen NH4+ that are present are oxidised into nitrates.
(3rd) Process - (Sedimentation)
The purified wastewater is separated from the activated sludge in the sedimentation tank and is conveyed into the wastewater disposal system via a discharge trough. The sedimentation tank (or Clarifier) is made of plastic and stainless steel, and it is inserted into the activation tank of the waste treatment plant. An airlift pump provides the re- circulation of the sludge from the sedimentation tank to the denitrification process, and at the same time skims off floating impurities from the sedimentation tank's surface.
1.0 BIOLOGICAL TREATMENT
1.1 Control of the aeration tanks
Fine-bubble aeration system serves as a source of air for the biological processes in the aeration tanks. The operation is controlled automatically in a pre-selected time regime - selected on Electronic controls located in the service box.
1.2 Technological regime and principle of aeration
The aeration tank has been designed for low load and high sludge age.
Sludge load is considered in a range of 0.08 - 0.12 kg BOD/kg.d. according to current load of the plant. The considered sludge age is 12 - 20 days according to actual load. The technological design envisages anaerobic separated stabilisation of sludge, with nitrogen removal by employing interrupted process of nitrification-denitrification (with the potential simultaneous precipitation of phosphorus as an extra).
1.3 Removal of carbonaceous removal
Degradation of carbonaceous pollution is the basic process of every biological wastewater treatment plant. This process is facilitated by a whole number of micro organisms that are normally present in activated sludge. Wastewater pollution serves as "food" for these micro organisms.
1.4 Biochemical oxygen demand (BOD)
BOD is defined as the amount of oxygen consumed by micro organisms for decomposing organic substances under aerobic conditions.
Determination of BOD must be carried out with suppressed nitrification.
1.5 Chemical oxygen demand
COD characterized the total oxygen consumption needed for oxidation of organic substances in the wastewater sample.
1.6 Loss of volatile compounds
Loss of volatile compounds characterizes the proportion of organic substances in respect of all substances.
1.7 BOD loading of sludge, sludge age
The basic technological parameter of the biological stage is the sludge load (kg BOD/kg.d.) characterizing how much organic load is conveyed to the plant in 1 day in relation to 1 kg of activated sludge in the aeration tank. Due to the fact that the treatment of wastewater is a biological process performed by present micro organisms, it is logical that the efficiency of these micro organisms is limited by the minimum need of substrate feeding supporting the vital reproduction processes on one hand, and maximum efficiency of pollution degradation, on the other hand. This treatment technology is dependant on maintaining organic load (Bx) at a level ranging from 0.08 to 0.12 kg BOD/kg.d. The optimum value is approx. 0.08 kg/kg.d. in cold periods and 0.10 kg/kg.d in summer periods. Due to the fact that the incoming organic load is not constant, the calculated load must be continuously evaluated.
Smaller quantities of sludge in the system are sufficient for lower BOD loads, based on the formula for BOD loading of sludge: in theory, the operational values of the concentration of activated sludge dry solids may range from 2 - 5 kg/m3.
The technological design of the plant considers a typical value for the given type of the aeration tank process, i.e. approx. 3.5 kg/m3. However, deviations within the stated range are permissible.
There is a principle that it is useless to keep unnecessarily high quantity of sludge in the system since this state deteriorates the economic parameters of the plant (e.g. useless re-circulation of sludge and useless oxygen supply needed for respiration of technologically excessive quantity of sludge).
Conversely, insufficient quantity of sludge in the system will not provide for the desirable treatment efficiency.
The next principle is that the biological activity of sludge increases in line with the temperature of wastewater. This relation must be traced individually for every plant. However, generally speaking, lower quantity of sludge in the system to dispose of the same BOD load is necessary in the summer season. Therefore, the adequate treatment efficiency can be maintained at higher BOD load, i.e. at reduced operation expenditures.
It is also necessary to draw attention to the relation between concentration of sludge in the aeration tank and the efficiency of secondary tanks - lower X value brings about drop in the amount of escaping sludge flocs from the secondary tanks, i.e. lower residual pollution at the effluent of the plant is achieved in most of the main monitored parameters.
The second basic technological parameter of biological treatment is the sludge age Qx. Given the employed treatment technology, the minimum sludge age should be 10 days in the summer period and 16 days in the winter period. Sludge age depends on the quantity of sludge in the system and the quantity of excess sludge withdrawn from the system.
It is obvious that the sludge age can be affected by the sludge withdrawals from the system. For each plant, it is possible to identify the optimum sludge age with respect to the treatment efficiency and economical operation. Again, it is true that smaller quantity of sludge in the system, i.e. younger sludge, is sufficient to maintain the same efficiency provided that the temperatures are higher.
The above description implies that, given a constant size of the aeration tanks, both the BOD load of sludge and sludge age, are mainly dependant on the concentration of sludge in the aeration tank (X). Sludge concentration is determined by the re-circulation proportion (Rc, %).
Generally, if the quality of sludge is constant, the increased re-circulation brings about higher sludge concentration in the aeration tank.
It is also true that given a constant re-circulation, the value of sludge concentration in the aeration tank changes in dependence on the quality of re-circulated sludge.
This implies that in order to maintain the prescribed sludge concentration in the aeration tank, it is necessary to monitor and know the quality of re-circulated sludge and selects the re-circulation proportion accordingly. The general rule is that in order to maintain the prescribed concentration of sludge with declining quality, it is necessary to increase the re-circulation proportion.
The basic operating indicator characterizing the quality of sludge is the so-called " sludge index " (KISVI). The sludge index characterizes the settling and thickening qualities of sludge.
Increasing sludge index indicates poorer qualities of sludge. The described principle implies that upon poorer settling and thickening of sludge, it is necessary to re-circulate greater volume of sludge in order to maintained the required sludge concentration.
The sludge index must be evaluated on regular basis, since it is one of the most important indicators for setting up the programme-controllable functions of the biological stage. Well-operating plants reach a KI value lower than 100 ml/g. Poorly performing plants may get up to a level of 200 ml/g. Even higher values indicate major failures and very poor quality of activated sludge.
The sludge index is determined in laboratories. The value of the so-called "sediment" is used as an informative indicator of the quantity and quality of sludge in small-sized plants. One litre of mixed liquor is taken from the aeration tank, poured into a gauged vessel with a volume of 1 litre. Here the sludge settles for 30 minutes. Afterwards, the volume of settled sludge is read. Values of approx. 300 - 400 ml are considered common.
2.0 SLUDGE VOLUME INDEX
If there is less settled sludge, the frequency of excess sludge withdrawals decreases. If the volume of settled sludge is greater, the frequency of excess sludge withdrawals rises.
The recommended range of the sediment value can be determined for the common sludge index of the specific plant to be evaluated in the testing operation.
The following relation applies for determination of the circulation proportion: where
During operation, we recommend that the adjustment should be carried out according to the following table stating the dependence of the re-circulation proportion (R) on the selected sludge concentration in aeration tank (X) and on the sludge index (KI)
The table shows the range of recommended values of the re-circulation proportion for the specific plant. The re-circulation proportion is related to the wastewater flowage through the plant: Qr = R * Qov
The required percentage of re-circulation will be achieved by the period of the re-circulation pump run. More frequent and longer running will result in higher re-circulation proportion. The frequency and period of the pump operation will be set on the Electronic controls located in the switchboard.
When withdrawing excess sludge, the pump operation is switched over to manual mode. The quantity of withdrawn excess sludge is determined by the period of pump operation according to the watch. Withdrawal of excess sludge should be carried out in smaller quantities, e.g. twice at the beginning and at the end of the working shift.
2.1 Sludge index
The sludge index is defined as a volume in millilitres taken up by 1 g of sludge dry solids after half an hour settling, where the sludge index expresses the settling and thickening properties of sludge.
2.2 Nitrogen removal and its forms
Nitrogen removal is designed as an interrupted process of nitrification and denitrification.
Major share of nitrogen at the influent consists of ammonia nitrogen (N-NH4) and partially, organic nitrogen (Norg), which is however quickly hydrolysed into the ammoniac form.
The form of nitrogen at the effluent of the plant is ammonia nitrogen (N-NH4), nitrate (N-NO3) and organic nitrogen (Norg).
Other forms of nitrogen are represented in small concentrations only.
2.3 Nitrification
Ammonia nitrogen is oxidized in the process of nitrification:
Nitrification is very stable and efficient for low-loading aeration tank processes.
Nitrification is an anoxic process requiring a supply of oxygen.
2.4 Denitrification
In the process of denitrification, there occurs reduction and decomposition of ammonia nitrogen:
Denitrification is an anoxic process - without oxygen supply, only agitating of the aeration tank.
FERRIC DOSING
2.5 Phosphorus degradation and its forms
Phosphorus will be degraded using simultaneous precipitation by Ferric, a solution of ferric sulphate.
From the technological viewpoint, it is necessary to monitor Pc and P-PO4.
2.6 Preparation and dosing of the precipitant
Dosing of Ferric does not require any special preparation of the precipitant. Ferric is supplied in a form of solution to be directly dosed in quantities determined by the design values or based on a laboratory test.
Concentration of dosed solution is 40 %.
Adding of precipitant: by dosing pump
2.7 FERRIC DOSING.
The balance of phosphorus at the influent and effluent of the plant govern ferric dosing - the balance is determined by analyses of wastewater. The balance implies the quantity of phosphorus in kg/l to be chemically degraded. The precipitant dose amounts to 1.5 mol Fe 3+/mol P, i.e.2.7 kg Fe3+/kg P.
The recalculation of demand of kg Fe3+/d with respect to the volumetric amount of Ferric is based on the content of 11 % Fe in 1 kg of Ferric and on the specific weight of Ferric, which is approximately 1,570 kg/m3.
3.0 ACTIVATED SLUDGE AND ITS CHARACTERISTICS
3.1 Sludge settle ability, measurement of the volume of settleable solids after 30 minutes
The measurement of the volume of settleable solids is carried out in a vessel with a volume of 1 litre for a period of 30 minutes. Samples are taken from the aeration tank sludge and re-circulated sludge. The volume of settleable sludge (in millilitres) is read after 30 minutes. This value is sometimes called "sediment". This is an indicative value for simple operational determination of the quantity of sludge in the system. High sediment indicates great quantity of sludge; low sediment indicates small quantity of sludge. This test is not accurate if the sludge has changeable characteristics, which is quite frequently so.
This is at the same time the test of settling and thickening features of sludge - being one of the basic tests serving as guidelines for the operation staff of the plant.
See chapter "Sludge index".
-3.2 Supernatant and its evaluation
Supernatant is understood as the layer of clean water at the surface level of the secondary sedimentation tank that flows out of the plant.
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Supernatant should consist of clean clear water without discoloration, without flocs of activated sludge and without mal-odour. The supernatant layer should be approx. 1 m thick.
-3.3 Sludge content in aeration tank, BOD loading
Adequate sludge content in the aeration tank is a pre-condition for proper operation of the biological stage of the plant. All operations performed by the staff are basically targeted at its optimising all year round.
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For details see "BOD loading of sludge, sludge age. (-1.8)
-3.4 Biological picture of the activated sludge
This determines the organisms present in the activated sludge.
The presence of fibrillar micro-organisms is undesirable.
-A specialist must conduct biological monitoring. After training, the basic monitoring can also be performed by the attendant of the plant.
-3.5 Unsuitable micro-organism's and causes of their occurrence
The presence of filamentous bacteria and froth-creating micro-organism's is particularly undesirable.
There are various causes for their presence - composition of wastewater, technological parameters of the process, lack of oxygen etc.
The evaluation is always subject to an expert microbiological report.
-3.6 Start-up of aeration tank
Filling of tanks
The tanks must be filled up with water evenly so that all functional tanks are filled in order to avoid collapsing of walls that are not dimensioned for water over-pressure due to differences in water levels in individual tanks.
3.7 Start-up without additional sludge
In order to fill the aeration tanks and secondary tanks up with wastewater, it is necessary to initiate the aeration tank process. This is carried out gradually. The wastewater influent is throttled; the remaining wastewater will be by-passed. Aeration and re-circulation of return sludge will be put into operation. Excess sludge will not be withdrawn. The Process Technician will determine the quantity of re-circulated sludge and the quantity of supplied wastewater - this will vary in the course of the process initiation. It is necessary to avoid both excess and lack of the substrate. Initiation of the aeration tank process requires intensified chemical-technological as well as microbiological supervision. Once the sludge volume in the aeration tank reaches approx. 100 ml/l, it is possible to process full wastewater influent.
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Removal of excess sludge is initiated after achieving the required sludge concentration in the aeration tank cell. The initiation of the aeration tank process conducted in this way takes several weeks.
-3.8 Start-up with additional sludge
The conditions for initiation of the process are similar; the difference being that fresh activated sludge from another similar plant is introduced into the aeration tank. Gradual loading of the system with wastewater, the re-circulation regime, withdrawal of excess sludge, aeration etc. are the same as in the previous case.
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This method of start-up requires approximately half the time. This mainly depends on the quantity of supplied sludge.
The process initiation can also be conducted with an addition of digested sludge. However, care must be taken especially with respect to maintaining aerobic conditions under any circumstances.
Note:
When starting up the plant, there may occur various adverse operating circumstances, such as generation of rich white froth. This is mainly due to the presence of detergents in wastewater. Once the activated sludge is created, this problem falls off.
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Over the start-up period, it is advisable to keep increased concentration of oxygen in the aeration tank system, i.e. a minimum of 2 - 3 mgO2/l.
-3.9 Signs of abnormal generation of activated sludge
Abnormal generation of sludge is mostly signalled by deteriorated treatment efficiency, whereas the filtered sample may show high efficiency and unfiltered sample may show reduced efficiency.
Visually, it is possible to observe discoloration of the supernatant, which is normally clear; poor-quality sludge is discoloured. It is also possible to see the escape of flocs from the secondary tank to the effluent of the plant.
Deteriorated quality of sludge is detected by the microbiological evaluation that should always be performed when there is a suspicion of forthcoming problems.
-3.10 Possibilities of regulating the characteristics and concentration of activated sludge
The characteristics and concentration of activated sludge can be primarily affected by elimination of adverse properties of wastewater by observing the sewerage code.
At the plant, the sludge characteristics can be affected by operational and technological discipline while building on previous experience with the operation gained in the periods of deteriorated sludge quality and it's improving.
-3.11 Aeration, recommended values of oxygen content
Recommended minimum oxygen concentration in the aeration tank: 2 mg/l
Recommended maximum oxygen concentration in the aeration tank: 4 mg/l
Lower than minimum concentration may bring about operational problems with the sludge quality and treatment efficiency.
Higher than maximum concentration will not cause operational problems; however, it is uneconomical (useless high performance of aerators).
Following start-up of the plant, it is possible to verify the minimum reliable values of the operational oxygen concentration as part of the testing operation. At some plants using this treatment technology, the nitrification is in progress even if the oxygen concentration is 1.5 - 1.0 mg/l.
-3.12 Oxygenation capacity of the system
The shape of the aeration tanks and the aerators throughput determines the oxygenation capacity of the system.
The calculated oxygenation capacity is 1.60 kgO2/h in standard conditions (10 oC). Note this is very very low usually we would expect > 2.5 kg) 2/kwhr
-3.13 Adjustment of air supply according to the operated aeration regime
Air is supplied in a time regime by actuating the blowers.
(OPTIONAL EXTRA'S)
1) Submersible mixer in the denitrification area.
2) Sludge Storage,- up to BC150
3) Oxygen Probe.
4) Ferric Dosing
5) PP Inspection Hatches
S.I. No. 249/2000: BUILDING REGULATIONS (AMENDMENT) (NO. 2) REGULATIONS, 2000
2000 239 S.I. No. 249 of 2000.BUILDING REGULATIONS (AMENDMENT) (NO. 2) REGULATIONS, 2000
STATUTORY INSTRUMENTS.
S.I. No. 249 of 2000.
BUILDING REGULATIONS (AMENDMENT) (NO. 2) REGULATIONS, 2000.
S.I. No. 249 of 2000.
BUILDING REGULATIONS (AMENDMENT) (NO. 2) REGULATIONS, 2000.
The Minister for the Environment and Local Government, in exercise of the powers conferred on him by Section 3 and 18 of the Building Control Act, 1990 (No. 3 of 1990) hereby makes the following Regulations:
1. These Regulations may be cited as the Building Regulations (Amendment) (No. 2) Regulations, 2000.
2. These Regulations and the Building Regulations, 1997 (S.I. No. 497 of 1997) and the Building Regulations (Amendment) Regulations, 2000 (S.I. No. 179 of 2000) shall be construed as one and cited together as the Building Regulations, 1997 to 2000.
3. These Regulations shall come into operation on the 1st day of January 2001.
4. Part D of the Second Schedule to the Building Regulations, 1997 (S.I. No. 497 of 1997) is hereby amended by the substitution of the following for Part D.
PART D MATERIALS AND WORKMANSHIP
Materials and Workmanship
D1 All works to which these Regulations apply shall be carried out with proper materials and in a workmanlike manner.
D2 A letter plate aperture shall be so positioned at a reasonable height above ground level as not to endanger the health and safety of persons using such apertures.
D3 In this Part "proper materials" means materials which are fit for the use for which they are intended and for the conditions in which they are to be used, and includes materials which-
(a) bear a CE Marking in accordance with the provisions of the Construction Products Directive; or
(b) comply with an appropriate harmonized standard, European technical approval or national technical specification as defined in article 4(2) of the Construction Products Directive; or
(c) comply with an appropriate Irish Standard or Irish Agrément Board Certificate or with an alternative national technical specification of any State which is a contracting part to the Agreement on the European Economic Area, which provides in use an equivalent level of safety and suitabillity.
"Agreement on the European Economic Area" means the Agreement on the European Economic Area between the European Communities, their Member States and the Republic of Austria, the Republic of Finland, the Republic of Iceland, the principality of Liechtenstein, the Kingdom of Norway, the Kingdom of Sweden and the Swiss confederation, as published in the Official Journal of the European Communities (OJ L1/9 of 3 January, 1994)."
GIVEN under the Official Seal of the Minister for the Environment and Local Government this 4th day of August, 2000.
NOEL DEMPSEY TD,
Minister for the Environment and Local Government.
EXPLANATORY NOTE.
(This note is not part of the Instrument and does not purport to be a legal interpretation.)
These Regulations amend Part D of the Building Regulations, 1997, by requiring that letter plate apertures shall be positioned at a reasonable height above ground level so as not to endanger the health and safety of persons using such apertures. These Regulations will apply to buildings commencing on or after 1 January, 2001.
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