OSO.90 - part 5 (translated)

5.5.3.2 Secondary Sedimentadora. The criteria of design for the secondary sedimentadores mustto determine itself experimentally.b. In absence of sedimentation tests, one is due to considerfollowing recommendations:- the design is due to carry out for hour maximum volumes;- for all the variations of the activated mud process(excluding prolonged ventilation) one recommends the following onesparameters:The hydraulic loads previously indicated are based onvolume of the residual water without considering the recirculation, sincesame it is retired of the bottom at the same time and it does not have influence inrate of climb of the sedimentador.c. For circular secondary decantadores they are due to considerfollowing recommendations:- the decantadores with capacities of up to 300 m3 can bedesigned without mechanism of type mud sweeping, having to beLOAD OFSURFACEm3/m2.dLOADkg/m2.hTYPE OFTREATMENTAverageMáx.AverageMáx.DEPTHmSedimentation acontinuation ofactivated muds(excludedventilationprolonged)16-3240-483,0-6,09,03,5-5Sedimentation acontinuation ofventilationprolonged8-1624-321,0-5,07,03,5-548conical or piramidal, with a minimum inclination of the walls ofhopper of 60 degrees (Dormund type). For these cases the removal ofmuds must be done through pipes with a minimum diameterof 200 mm.- the circular decantadores with mechanism of mud sweepingthey must be designed with a central hopper for mud accumulationof at least 0.6 ms of diameter and Maxima depth of 4 ms.The walls of the hopper must have an inclination of at least60 degrees.- the bottom of the circular decantadores must have an inclinationof around 1:12 (vertical one: horizontal).- the diameter of the zone of entrance in the center of the tank must beapproximately 15 to 20% of the diameter of the decantador. walls of the entrance well do not have to be deepened more than 1 mbelow the surface to avoid the drag muds.- the tip speed of the sweeping one of muds must beincluded/understood between 1.5 to 2.5 m/min and nongreater of 3 revolutionsfor hour.d. The rectangular secondary decantadores will be the second optionafter the circular ones. For these cases one is due to considerfollowing recommendations:- wide the long relation/must be 4/1 like minimum.- the wide relation/depth must be included/understood between 1 and2.- For the small facilities (up to 300 m3) it will be possible to be designedrectangular sedimentadores without mechanisms of mud sweeping,in which case inverted pyramids with angles will be designedminimums of 60º with respect to the horizontal.e. For oxidation ditches the design of the ditch is admitted withbuilt-in secondary sedimentador, for which the designer will haveto justify the design criteria properly.f. In order to facilitate the mud return, the following ones are due to considerrecommendations:- For circular decantadores, the return of mud will be continuous andit will be able to use centrifugal pumps or of positive displacement. installed capacity of the pumping station of return mudshe will be at least 100% over the operational capacity. pumping capacity will be sufficiently flexible (with motors ofvariable speed or number of pumps) so that it canto operate the plant in all the conditions throughout the life ofit plants.- For rectangular decantadores with mechanism of sweeping ofmovement toward the front, will consider the mud removal init forms intermittent, between periods of trips of the mechanism.- the return mud must be pumped to a distribution camera49with manual floodgates and garbage dumps to separate the mud ofexcess.- Alternatively the process can be controlled unloading mudof excess directly of the ventilation tank, using the age ofmud like control parameter. For example if the age of mud isof 20 days, 1/20 of the volume of the tank will be due to reject ofventilation every day. This is the only form of operation in the caseof ditches of oxidation with built-in sedimentador. In this casethe mixed licor must be retired in intermittent form (from 6 to 8retirements) to a tank of concentration (in the case of ditch ofoxidation) or to a espesador, in the case of other systems of lossage of mud.5.5.3.3 Ditches of oxidationa. The oxidation ditches are adapted for small and greatcommunities and constitute a special form of prolonged ventilationwith low costs of installation inasmuch as the use is not necessary ofprimary movement and the mud stabilized in the process can beemptied directly in drying beds. This type of treatmentit is in addition to simple operation and able to absorb variations abruptof load.b. The criteria of design for the oxidation ditches are such thatwhich has been enunciated in the previous chapter (activated muds) init refers parameters of design of the reactor and secondary sedimentador andrequirements of I oxygenate. In the present I capitulate occur recommendationsadditional own of this process.c. For the populations of up to 10000 inhabitants they are possible to be designedditches of conventional type, with horizontal rotors. For this caseit must consider the following recommendations:- the form of the conventional ditch is made oval, with a simple onepartition of soportante level in half. For a suitable onedistribution of the lines of flow, recommends the installation ofat least two located semicircular partitions inends, to 1/3 of the wide one of the channel.- the entrance can be a simple tube with free unloading, locatedpreferably before the rotor. If it is had more than two ditchesit will have to consider a box of distribution of volumes.- the horizontal rotor to select itself must be of so characteristic thatallow the circulation of the liquid with a speed of at least25 cm/seg. In this case the depth of the ditch will not have to begreater of 1.50 ms for a suitable transference at the moment. Nothe deepening of the channel underneath the zone is necessary ofventilation.- the rotors are cylindrical bodies of several types, supported inboxes of bearing in its ends, thus its lengthit depends on the structure and stability of each model. It stopsrotors of greater length of 3.0 ms the use of supports is recommendedintervals. The supports in the ends must have50obligatorily boxes of autoalineantes, able buns ofto absorb the deflections of the rotor without causing mechanical problems.- the determination of the characteristics of the rotor like diameter,length, speed of rotation and depth of immersion, mustto take place so that the requirements can be provided ofoxygen to the process in all the possible operative conditions.To the effect one is due to have the curves characteristic ofyield of the model considered in conditions standard. standard yields of horizontal rotors are of the order of1,8 to 2.8 kg O2/Kwh.- the normal procedure is to design the first garbage dump of exitof the ditch, the same one that can be of fixed or adjustable height andto determine the interval of immersions of the rotor for the different onesconditions of operation.- For facilities of up to 20 l/s can be considered the use ofditches of intermittent operation, without secondary sedimentadores.In this case storage is due to provide with the remainder byperiod of up to 2 hours, or in the interceptor or a ditchaccessory.- the motor-reducing set must be chosen in such a way thatspeed of rotation is between 60 and 110 RPM and that the speedperipheral of the rotor m/s is around 2.5.d. For greater populations of 10000 inhabitants one will be due to considerobligatorily the ditch of deep oxidation (reactor of orbital flow)with aeradores of vertical axis and low speed of rotation. Theseaereadores have the characteristic to transfer to the liquid mass init forms efficient so that they distribute a suitable speed and a flowof helical type. For this case they are due to considerfollowing recommendations:- the depth of the ditch will be of 5 ms and the wide one of 10 ms likemaximum. The density of energy will have to be superior to 10 W/m3- the reactors can have varied forms, wheneverlocate the aeradores in the ends and tangential form toseparation partitions. They occur as it guides following the wide ones anddepths of the channels:Equivalent inhabitants Wide, m Depth, m10000 5.00 1,5025000 6.25 2,0050000 8.00 3,5075000 8.00 4,00100000 9.00 4,50200000 10.00 5,00In relation to the form of the channels the following ones occurrecommendations:51- the depth of the channel must be between 0.8 and 1.4 times the diameterof the selected rotor;- the wide one of the channels must be between 2 and 3 times the diameter ofselected rotor;- the developed length of the channel does not have to exceed 250 ms;For the aereadores of vertical axis the following ones occurrecommendations:- the speed of rotation for the small aereadores must be of36 to 40 RPM and for the great aereadores of 25 to 40 RPM.- the distance between the aim of the dividing partition and the ends ofimpeller vanes must be around 1.5% of the total diameter ofrotor (including the trowels).- the depth of immersion of the rotor must be of 0.15 to 0.20 ms.- the density of energy in the zone of total mixture must be of 20 a60 W/m3.Ditches of oxidation of continuous operation can be consideredwith zones of denitrificación before a zone of ventilation. Foreffect is necessary to consider the following aspects:- In the design of secondary sedimentadores, for ditches withdenitrificación is due to assure a fast retirement mud, stopsto prevent the flotation of the same one.- the exit garbage dump must be located at the end of the zone ofdenitrificación.5.5.4 Percoladores filters5.5.4.1 The percoladores filters will have to be designed so that it is reduced to the minimumthe use of mechanical equipment. For it one will prefer the following onesoptions: stone beds, distribution of the primary efluente (treated inImhoff tanks) by means of fuzes or mechanisms of whirling armself-propelled, sedimentadores secondary without mechanisms of sweeping (withmud hoppers) and return of secondary mud to the primary treatment.5.5.4.2 The previous treatment to the percoladores filters will be: sieves, desarenadores andprimary sedimentation.5.5.4.3 The filters could be of discharge or low load, for which they will be had inconsideration the following parameters of design:Type of loadParameterLow DischargeHydraulic load, m3/m2/d 1.00 - 4.00 8,00 - 40,00Laid-down load, kg DBO/m3/d 0.08 - 0.40 0.40 - 4,80Depth (stone bed), m 1.50 - 3.00 1.00 - 2,00(average plastic), m Up to 12 msReason of recirculation 0 1.00 - 2,00525.5.4.4 In the filters of low load the metering must take place by means ofsiphons, with an interval of 5 minutes. For the filters of high loadmetering is continuous by effect of the recirculation and in case of being usedsiphons, the metering interval will be inferior of 15 seconds.5.5.4.5 Any system of distribution will be used that guarantees the distributionuniform of the primary efluente on the surface of contact means.5.5.4.6 When fixed fuzes are used, it will be located them in the vertices of trianglesequilateral that covers all the surface with the filter. The sizing ofpipes will depend on the distribution, the one that can be intermittent or continuous.5.5.4.7 Any means of contact will be allowed that promotes the development ofgreater amount of Biopelícula and that allows the free circulation of the liquid and ofair, without producing obstructions. When small stones are used,minimum size will be of 25 mm and the maximum of 75 mm. For great stones,its size will oscillate between 10 and 12 cm.5.5.4.8 A ventilation system will be designed so that a circulation existsnatural of the air, by temperature difference, through the system of drainageand through the contact bed.5.5.4.9 The drainage system must fulfill the following objectives:• to provide a hardware to means with contact;• to collect the liquid, for which the bottom must have a slope between1 and 2%;• to allow an suitable air recirculation.5.5.4.10 The drainage system will have to fulfill the following recommendations:• The channels of water harvesting will have to work with a bracemaximum of 50% in relation to its Maxima conduction capacity, andfor minimum braces it will have to ensure speeds drag.• Wells of ventilation in the ends of the central channel must be located ofventilation.• In case of filters of great surface wells must be designed ofventilation in the periphery of the unit. The surface opened of thesewells m2 by each 250 will be of 1 m2 of bed surface.• The false bottom of the drainage system will have a nonsmaller area of orificesto 15% of the total area of the filter.• In filters of low load without recirculation, the drainage system will haveto design itself so that the bed can be flooded to controldevelopment of insects.5.5.4.11 Facilities of secondary sedimentation are due to design. The intention ofthese units are to separate the biomass in excess produced in the filter. design could be similar to the one of the primary sedimentadores with the conditionof which the design load is based on the flow of the plant plus the flow ofrecirculation. The surface loading does not have to exceed 48 m3/m2/d based onthe maximum volume.535.5.5. Rotating Biological systems of Contact5.5.5.1 They are units that have means of contact placed in modules discs orcylindrical modules that rotate around their axis. The modules discs orcylindrical they are submerged generally up to 40% of his diameter, ofway that when rotating allows that the Biopelícula is put in contactalternadamente with the primary efluente and the air. The conditions ofapplication of this process is similar to those of the biological filters in whichone talks about efficiency.5.5.5.2 Necessarily the previous treatment to the biological systems of contactit will be: sieves, desarenadores and primary sedimentador.5.5.5.2 The rotatory modules can have following means of contact:• wood discs, located plastic material or metal in parallel formso that they provide a high faying surface for the developmentof the Biopelícula;• stuffed cylindrical meshes of light material.5.5.5.4 For the design of these units it will be observed the following onesrecommendations:• hydraulic load between 0.03 and 0.16 m3/m2/d.• the tip speed of rotation for municipal residual watersm/s must stay around 0.3.• the minimum volume of the units must be of 4.88 liters by each m2of contact means surface.• for modules in series a minimum of four units will be used.5.5.5.5 The efluente of these systems must treat in a secondary sedimentadorin order to separate the originating biomass of the biological reactor. The criteria ofdesign of this unit is similar to those of the secondary sedimentador ofbiological filters.5.6 Other Types of Treatment5.6.1 Application on the land and reuso agriculturist5.6.1.1 The application in the pretreated residual water land is a type oftreatment that can or not to produce a final efluente. If agriculturist exists reusoone will be due to fulfill the requirements of the effective legislation.5.6.1.2 The study of feasibility of these systems must include the aspects agricultural andof grounds considering at least the following thing:• ground evaluation: problems of salinity, infiltration, drainage, watersunderground, etc.;• evaluation of the quality of the water: possible problems of toxicity,tolerance of cultures, etc.;54• types of cultures, forms of irrigation, necessities of storage,infrastructure works, costs and yield.5.6.1.3 The three main processes of application in the land are: irrigation to rateslow, fast infiltration and superficial flow.5.6.1.4 For systems of irrigation of slow rate the following parameters are suggested ofdesign:to Grounds will be chosen that have a good drainage and a permeability nogreater of 5 cm/d.b. Slope of the land: for cultures 20% at the most and forestsup to 40%.c. Depth of napa phreatic: minimum 1.5 ms and preferably more of3 ms.d. Required pre-cure: according to the lineamientos of the previous numeral.and Requirements of storage: one is due to analyze carefullycarrying out a hydric balance. The variables to consider itself are byless:- infiltration capacity- rain regime- type of ground and culture- evapotranspiración and evaporation- applicable hydraulic load- periods of rest- additional treatment that takes place in the storage.f. The nitrogen load will be verified so that when carrying out the balancehydric, the calculated nitrate concentration in underground watersmg/l is inferior of 10 (like nitrogen).g. The laid-down load will be between 11 and 28 kg DBO/(ha.d), to preventexaggerated development of biomass. The low loads will be used withsecondary efluentes and the high loads with primary efluentes.h. The periods of rest usually it varies between 1 and 2 weeks.i. For defense of the quality of the underground water the cultures will be preferredwith high nitrogen use.5.6.1.5 For the systems of fast infiltration the following ones are recommendedparameters:to Grounds able are required 60 to infiltrate from 10 to cm/d, like sand,the sandy slime, muddy sands and burden fine. It is also requiredsuitable knowledge of the variations of the phreatic level.b. The required pre-cure is primary like minimum.c. The water table must be between 3 and 4.5 ms of depth like minimum.d. The hydraulic load can vary between 2 and 10 cm per week,depending on several factors.and The necessary storage is due to determine considering55variables indicated in the previous numeral. One is due to maintain periodsof rest between 5 and 20 days to maintain conditions aerobic inground. The periods of application will be chosen maintaining onerelation between 2:1 to 7:1 between the rest and application.f. The recommended laid-down load must stay between 10 and 60 kgDBO/(ha.d).