OSO.90 - part 3 (translated)

5.1.5 The systems of lagoons must be located in a sufficiently extensive area andoutside the influence of subject channels to torrents and avenues, and in the case ofnot to be possible, protective installations will be due to project. The area will have to bethe most moved away possible of the populated centers, recommending itselffollowing distances:_ 500 ms like minimum for anaerobic treatments;_ 200 ms like minimum for facultative lagoons;_ 100 ms like minimum for systems with aeradas lagoons; and_ 100 ms like minimum for activated muds and percoladores filters.The distances must be justified in the study of environmental impact. project must consider an area of protection around the system oftreatment, determined in the study of environmental impact.The designer will be able to justify smaller distances to the recommended ones ifhe includes in the design processes of control of scents and other contingenciesdetrimental.5.1.6 From item 5,2 in ahead the criteria are detailed that will be used stopsthe sizing of the treatment units and structurescomplementary. The values that are included are referential and arebased on the state-of-the-art of the technology of water treatmentresidual and they could be modified by the previous designer presentation, tocompetent authority, of the justification sustentatoria based oninvestigations and the technological development. The results ofinvestigations made in the local level could be incorporated to the normwhen this one is updated.5,2 Works of arrival5.2.1 To the set of structures located between the distributing point of the emitter andprocesses of preliminary treatment denominate arrival structures to him. In24general terms these structures must be determine the proportions for the volumemaximum schedule.5.2.2 A structure of reception of the emitter will be due to project that allowsto obtain suitable speeds and to dissipate energy in the case of lines ofimpulsion.5.2.3 Immediately after the reception structure it will be locateddevice of deflection of the plant. The existence, size and considerations ofdesign of these structures will be justified properly consideringprocesses of the plant and the operation in conditions of maintenancecorrective of one or several of the processes. For stabilization lagoonsthey will have to project these structures for the periods of drying and removalof muds.5.2.4.1 The location of the pumping station (in case of existing) will depend on the typeof the pump. For the case of pumps of the type screw, this can beplaced before the preliminary treatment, preceded of heavy sieves with onesmaller opening to the spiral passage. For the case of centrifugal pumps withoutdisintegrator, the pumping station will have to be located after the process ofsifting.5,3 Preliminary treatmentThe units of preliminary treatment that can be used in the treatmentof municipal residual waters they are the sieves and the desarenadores.5.3.1. Sieves5.3.1.1 The sieves must be used in all plant of treatment, even in the plusessimple.5.3.1.2 Sieves of manual cleaning will be designed preferredly, unlessamount of sifted material justifies those of mechanized cleaning.5.3.1.3 The design of the sieves must include:_ a platform of operation and drainage of the material sifted with railingsof security;_ illumination for the operation during the night;_ sufficient space for the temporary storage of the sifted materialin suitable sanitary conditions;_ technical solution for the final disposition of the sifted material; and_ the floodgates necessary to put outside operationanyone of the units.5.3.1.4 The design of the channels will take place for the conditions of maximum volumeschedule, being able to consider the following alternatives:25_ three channels with sieves of equal dimension, as which one will serve asby pass in case of emergency or maintenance. In this case two ofthe three channels will have the capacity to lead the maximum schedule;_ two channels with sieves, each one determine the proportions for the maximum volumeschedule;_ for small facilities can be used a channel with sieves with bypass for the case of emergency or maintenance.5.3.1.5 For the design of sieves of grates the following ones will be taken into accountaspects:a) Bars of rectangular section of 5 to 15 mm of thickness will be used of30 to 75 mm wide. The dimensions depend on the length ofI sweep and the cleaning mechanism.b) the espaciamiento between bars will be between 20 and 50 mm. For localitieswith an inadequate system of harvesting of solid remaindersit recommends a espaciamiento nongreater to 25 mm.c) the dimensions and espaciamiento between bars will be chosen of waythat the speed of the channel before and through the bars isadapted. The speed through the clean bars must staybetween 0.60 to 0.75 m/s (based on hour maximum volume). speeds must be verified for the minimum volumes, average andmaximum.d) Determined the dimensions will be come to calculate the speed ofchannel before the bars, the same one that must stay between 0.30 and0,60 m/s, being 0.45 m/s a value commonly used.e) In the determination of the hydraulic profile the pressure drop a will calculatetraverse of the sieves for conditions of hour maximum volume and 50%of the obstructed area. The obtained most unfavorable value will be used toto apply the correlations for the calculation of pressure drop. The brace ofwater in the channel before the sieves and the free edge will be verified stopsconditions of hour maximum volume and 50% of the area of sievesobstructed.f) the rake of the bars of the sieves of manual cleaningit will be between 45 and 60 degrees with respect to the horizontal.g) the calculation of the amount of sifted material will be determined in agreementwith the following table.Opening(mm)Amount (liters of materialsifting l/m3of residual water)20 0,03825 0,02335 0,0122640 0,009h) to facilitate the installation and the maintenance of the cleaning sievesmanual, the grates will be installed in lateral guides with profilesmetalists in “U”, resting at heart in a profile “L” or ontop formed by a small launching slip of concrete.5.3.2 Desarenadores5.3.2.1 The inclusion of desarenadores is obligatory in the plants that they havesedimentadores and digestores. For systems of stabilization lagoonsuse of desarenadores is optional.5.3.2.2 The desarenadores will be preferredly of manual cleaning, without incorporatingmechanisms, except in the case of desarenadores for facilitiesgreat. According to the removal mechanism, the desarenadores can be agravity of horizontal or helical flow. First they can be designedas channels of extended form and rectangular section.5.3.2.3 The desarenadores of horizontal flow will be designed to remove particlesof average diameter equal or superior to 0.20 mm. For the effect one is due to treatto control and to maintain the speed of the flow around 0.3 m/s with onetolerance + 20%. The rate of application will have to be between 45 and 70 m3/m2/h,having to verify itself for the conditions of the place and the maximum volumeschedule. When coming out and entered of the desarenador it will be anticipated, to each side, byexcept an additional length equivalent to 25% of the theoretical length. relation between the length and the height of the water must be like minimum 25. The heightof the water and free edge it must be verified for the hour maximum volume.5.3.2.4 The control of the speed for different water braces will take place withinstallation of a garbage dump when coming out of the desarenador. This it can be of typeproportional (sutro), trapezial or a measurer of critical regime (Parshall orPalmer Bowlus). The speed must be verified for the minimum volume,average and maximum.5.3.2.5 Two units are due to provide with alternating operation like minimum.5.3.2.6 For desarenadores of manual cleaning the facilities are due to includenecessary (floodgates) to put outside operation anyone ofunits. The dimensions of the part destined to the sand accumulationthey must be determined based on the anticipated amount of material andfrequency of wished cleaning. The minimum frequency of cleaning will be ofonce for week.5.3.2.7 The desarenadores of hydraulic cleaning are not recommendable unlessadditional facilities for the drying of the sand are designed (pools orlagoons).5.3.2.8 For the design of desarenadores of helical flow (or Geiger), the parametersof design properly they will be justified before the competent organism.275.5.3.3 Measurer and Distributors of Volume5.3.3.1 After the sieves and desarenadores one is due to include in obligatory formmeasurer of volume of critical regime, being able to be of the type Parshall or PalmerBowlus. The use of garbage dumps will not be accepted.5.3.3.2 The volume measurer must include a well of registry for the installation oflimnígrafo. This mechanism must be installed in a house withappropriate safety measures.5.3.3.3 The structures of volume distribution must allow the distribution ofvolume considering all its variations, in proportion to the capacity ofinitial process of treatment for the case of the conventional treatment and inproportion to the areas of the primary units, in the case of lagoons ofstabilization. In general these facilities do not have to allow the accumulationof sand.5.3.3.4 The distributors can be of the following types:_ camera of distribution of central entrance and ascending flow, withcircular or square garbage dump and installation of manual floodgates,during conditions of medium repair._ distributing with partitions in critical regime, the same one that will be located inchannel._ others properly justified before the competent organism.5.3.3.5 For the facilities before indicated the design one will take place forconditions of hour maximum volume, having to verify hisoperation for conditions of minimum volume at the beginning of the operation.5,4 Primary Treatment5.4.1 Majorities5.4.1.1 The objective of the primary treatment is the organic solid removal einorganic sedimentables, to diminish the load in the biological treatment.The solids removed in the process process must be before hisfinal disposition.5.4.1.2 The processes of the primary treatment for residual waters can be:Imhoff tanks, tanks of sedimentation and tanks of flotation.5.4.2 Imhoff Tanks5.4.2.1 They are tanks of primary sedimentation in which the digestion is gotten upof muds in a compartment located in the inferior part.5.4.2.2 For the design of the zone of sedimentation it will be used the following criteria:a) The area required for the process will be determined with a load28superficial of 1 m3/m2/h, calculated on the basis of of great volume means.b) the period of nominal retention will be of 1.5 to 2.5 hours. The depthit will be the product of the surface loading and the period of retention.29c) the bottom of the tank will be of cross-sectional section in form of V andslope of the sides, with respect to the horizontal axis, will have between 50 and60 degrees.d) In the central edge will leave an opening for the solid passage of0,15 ms to 0.20 ms. One of the sides will have to extend so thatprevent the gas passage towards the sedimentador; this prolongation will haveto have a horizontal projection of 0.15 to 0.20 ms.f) the free edge will have a minimum value of 0,30m.g) the structures of entrance and exit, as well as other parameters ofdesign, will be such that for the rectangular sedimentadoresconventional.5.4.2.3 For the design of the compartment of storage and mud digestion(zone of digestion) one will consider the following criteria:a) The volume muds will be determined considering the reduction of 50% ofvolatile solids, with a density of 1.05 kg/l and a content averageof 12.5% solids (to the weight). The compartment will be determine the proportionsin order to store muds during the process of digestion according totemperature. The following values will be used:TEMPERATURE (ºC)TIME OFDIGESTION (DAYS)5110107615552040_ 2530b) Alternatively will determine the volume of the mud compartmentconsidering a volume of 70 liters by inhabitant for the temperatureof 15ºC. For other temperatures this unitary volume mustto multiply by a factor of relative capacity according to the values ofthe following table:30to peak altitude of muds it will have to be 0.50 ms below the bottom ofsedimentador.d) the bottom of the compartment will have the form of a pyramid trunk,whose walls will have an inclination of 15º to 30º with respect tohorizontal.5.4.2.4 For the design of the free surface between the walls of the digestor and the ones ofsedimentador (zone of foam) the following criteria will be followed:a) The free espaciamiento will be of 1.00 ms like minimum.b) total the free surface will be at least 30% of the total surface oftank.5.4.2.5 The facilities for the digested mud removal must be designed init forms similar the primary sedimentadores, considering that muds areretired for drying in intermittent form. For the effect they are due to have init counts the following recommendations:a) The minimum diameter of the pipes of mud removal will be of 200mm.b) the pipe of mud removal must be 15 cm over the bottomof the tank.c) For the hydraulic removal of mud requires at least one loadhydraulics of 1.80 ms.5.4.3 Tanks of Sedimentation5.4.3.1 The small tanks of sedimentation, of diameter or nongreater side mustto be projected without mechanical equipment. The form can be rectangular,to circulate or square; the rectangular ones will be able to have several hoppers andcircular or square a central hopper, as it is the case ofsedimentadores Dormund type. The inclination of the walls of the hoppers will beof at least 60 degrees with respect to horizontal. The parameters ofdesign is similar to those of sedimentadores with mechanical equipment.TEMPERATURE (ºC)CAPACITY FACTORRELATIVE52,0101,4151,0200,7> = 250,5315.4.3.2 The greater tanks of sedimentation will use mechanical equipment formud sweeping and transport to the processes of mud treatment.5.4.3.3 The parameters of design of the tank of primary sedimentation and hisefficiencies must preferredly be determined experimentally.When conventional tanks of primary sedimentation are designed withoutexperimental datas will be used the following criteria of design:a) The channels of distribution and entrance to the tanks must be designedfor the hour maximum volume.b) the area requirements must be determined using surface loadingsbetween 24 and 60 m/d based on of great volume means of design, which is equivalentat a speed of sedimentation from 1.00 to 2.5 m/h.c) the period of nominal retention will be of 1.5 to 2.5 hours (recommendable <2 hours), based on the daily maximum volume of design.d) the depth is the product of the surface loading and the period ofretention and must be between 2 and 3.5 m.s (recommendable 3 ms).e) Wide the long relation/must be between 3 and 10 (recommendable 4) andlong relation/depth between 5 and 30.f) the hydraulic load in the 500 garbage dumps will be from 125 to m3/d by meterlinear (recommendable 250), based on the daily maximum volume of design.g) the efficiency of removal of the sedimentation process can be consideredin agreement with the following table:Recommended percentage of removalPeriod of retentionnoun (hours)200 DBO 100 to 300 mg/l DBO 200 to mg/lDBO SS * DBO SS *1,5 30 50 32 562,0 33 53 36 603,0 37 58 40 644,0 40 60 42 66Total solid SS * = in suspension.h) the volume of primary muds must calculate for the end of the period ofdesign (with of great volume means) and to evaluate itself for every 5 years of operation.The solid removal of the process will be obtained from the following table:Solid concentrationType of mudprimaryGravitySpecific Rank%RecommendedWith sewage systemtoilet1,03 4 - 12 6,0With sewage systemcombined1,05 4 - 126,5With activated mudof excess1,03 3 - 104,032i) the retirement of muds of the sedimentador must take place in cyclical form eideally by gravity. Where it is not had hydraulic loadit must retire by pumping in cyclical form. For primary mudit recommends:_ rotating pumps of positive displacement;_ diaphragm pumps;_ piston pumps; and_ centrifugal pumps with open impeller.For a suitable operation of the plant, he is recommendable to installcyclical motors of variable speed and each 0.5 switches who work a4 hours. The system of mud conduction will be able to include, of being necessary,device to measure the volume.j) the volume of the mud hopper must be verified formud storage of two consecutive cycles. The speed inpipe of exit of primary mud must be at least 0.9 m/s.5.4.3.4 The mechanism of mud sweeping of rectangular tanks will have onespeed between 0.6 and 1.2 m/min.5.4.3.5 The characteristics of the circular tanks of sedimentation will befollowing:_ depth: of 3 to 5 ms_ diameter: of 3.6 to 4.5 ms_ pending of bottom: from 6% to 16% (recommendable 8%).5.4.3.6 The mechanism of mud sweeping of the circular tanks will have oneincluded/understood tangential tip speed between 1.5 and 2.4 m/min or onespeed of rotation of 1 to 3 revolutions per hour, being two a valuerecommendable.5.4.3.7 The system of entrance to the tank must guarantee the uniform distribution ofliquid through the cross-sectional section and must be designed so in form thatavoid short circuits.5.4.3.8 The hydraulic load in the exit garbage dumps will be from 125 to 500 m3/d bylinear meter (recommendable 250), based on the daily maximum volume of design.5.4.3.9 A system of harvesting of creams will be due to design, the ones that mustto store itself in a special well before being transported to the process ofdigestion.5.4.3.10 The minimum slope of the 1.7 mud hopper will be vertical to 1.0 horizontal. Incase of rectangular sedimentadores, when the hopper is too muchwide, a cross-sectional one will be due to provide sweeping from the end topoint of mud extraction.335.4.4 Tanks of FlotationThe flotation process is used in residual waters to remove particlesfine in suspension and of low density, using the air like agent offlotation. Once the solids have been elevated to the surface of the liquid,they are removed in a skimmed operation of. The process requires the greater onemechanization degree that the conventional tanks of sedimentation; hisuse will have to be justified before the competent organism.5,5 Secondary Treatment5.5.1 Majorities5.5.1.1 For effects of the present norm of design they will be considered likesecondary treatment the biological processes with a removal efficiencyof soluble DBO greater to 80%, being able to be of biomass in suspension oradhered biomass, and includes the following systems: stabilization lagoons,activated muds (including the ditches of oxidation and other variants), filtersbiological and rotatory modules of contact.5.5.1.2 The selection of the type of secondary treatment, will have to be properlyjustified in the feasibility study.5.5.1.3 Between the methods of biological treatment with biomass in suspensionthey will prefer those that are of easy operation and maintenance and thatreduce to the minimum the use of complicated mechanical equipment or that nocan be repaired locally. Between these methods they are the systems ofstabilization lagoons and the ditches of oxidation of intermittent operation andcontinuous. The activated mud system conventional and the compact plantsof this type they could be used only in the case in that one demonstrates thatother inconvenient alternatives are technique and economically.5.5.1.4 Between the methods of biological treatment with adhered biomass they will be preferredthose that are of easy operation and that they lack complicated equipment orof difficult repair. Among them they are the percoladores filters and the modulesrotatory of contact.5.5.2 Lagoons of Stabilization5.5.2.1 General Aspectsa. The stabilization lagoons are pools designed forresidual water treatment by means of natural biological processesof interaction of the biomass (seaweed, bacteria, protozoarios, etc.) andcontained organic matter in the residual water.b. The treatment by stabilization lagoons is applied when the biomassof the seaweed and the nutrients that unload the efluente they can beassimilated by the receiving body. The use of this type of treatmentit recommends specially when a high degree of removal is required34of pathogenic organisms.For the cases in which the efluente is unloaded to a lake ordam, will have to evaluate the possibility of eutroficación of the bodyreceiver before its consideration like alternative of unloading or inall case is due to determine the postratamiento necessities.c. For the domestic and industrial residual water treatmentthey will consider solely the systems of lagoons that you have unitsanaerobic, aeradas, facultative and of maturation, in the combinationsand number of units that are detailed in the present norm.d. The discharge lagoons will not be considered like treatment alternativeproduction of biomass (known like aerobic lagoons orphotosynthetic), because its purpose is to maximize the production ofseaweed and not the treatment of the liquid remainder.5.5.2.2 Anaerobic Lagoonsa. The anaerobic lagoons are used generally like first unitof a system when the land availability is limited or fordomestic residual water treatment with high concentrations andindustrial remainders, in which case can occur several unitsanaerobic in series. The use is not recommendable anaerobic lagoonsfor 15 smaller temperatures of ºC and presence of high content ofsulphates in residual waters (greater to 250 mg/l).b. Due to the high loads of design and to the reduced efficiency, it isnecessary the additional treatment to reach the treatment degreerequired. In the case of using secondary facultative lagoons hissuperficial laid-down load does not have to be over the values limitfor facultative lagoons. Generally the area of the units in seriesof the system it does not have to be uniform.c. In the sizing of anaerobic lagoons it is possible to be usedfollowing recommendations for 20 temperatures of ºC:_ volumetric laid-down load from 100 to 300 g DBO/(m3.d);_ period of nominal retention of 1 to 5 days;_ depth between 2,5 and 5 ms;_ 50% of efficiency of DBO removal;_ greater surface loading of 1000 kg DBO/ha.día.d. A minimum number of two units in parallel will be due to design stopsto allow the operation in one of the units while mud is removedof the other.e. The mud accumulation will calculate with a nonsmaller contribution of 40l/hab/año. One will be due to indicate, in the descriptive and manual memory ofoperation and maintenance, the period of cleaning assumed in the design.35In no case the volume of accumulated muds will be due to allow thatsurpass 50% of the brace of the lagoon.f. For effects of the calculation of the bacterial reduction one will be assumednull reduction in anaerobic lagoons.g. It will have to verify the values of volumetric laid-down load and loadssuperficial for the conditions of beginning of operation and cleaning ofmuds of the lagoons. These values must be included/understood betweenrecommended in point 3 of this article.