OSO.90 - part 4 (translated)

5.5.2.3 Aeradas Lagoonsa. The aeradas lagoons are used generally like first unit ofa treatment system in where the availability of the land islimited or for the treatment of domestic remainders with dischargesindustrial concentrations or remainders whose residual waters arepredominantly organic. The use of the lagoons aeradas in serieshe is not recommendable.b. The following types of aeradas lagoons are distinguished:_ aeradas Lagoons of complete mixture: the same ones that maintainsbiomass in suspension, with a HD of installed energy(> 15 W/m3). They are considered like a incipiente mud processactivated without separation and mud recirculation and the presence ofseaweed is not apparent. In this type of lagoons the depth variesbetween 3 and 5 ms and the period of retention between 2 and 7 days. For theseunits the use of aeradores of low speed is recommendable ofrotation. This it is the only case of aerada lagoon for which it existsa sizing methodology._ facultative aeradas Lagoons: which maintain the biomass inpartial suspension, with a density of installed energy smaller thanthe previous ones (1 to 4 W/m3, recommendable 2 W/m3). This type oflagoon presents/displays mud accumulation frequently, being observedthe appearance of gas bubbles of great size in the surface byeffect of the mud digestion at heart. In this type of lagoonsthe periods of retention vary between 7 and 20 days (variation averagebetween 10 and 15 days) and the depths are at least 1.50 ms. Inwarm climates and with good insolation an appreciable one is observedgrowth of seaweed in the surface of the lagoon._ facultative Lagoons with mechanical agitation: they are appliedto units exclusively overloaded of the facultative type inwarm climates. They have one lowers density of energy installed (oforder of 0.1 W/m3), the same one that serves to overcome the effectsadverse of the thermal stratification, in absence of the wind. conditions of design of these units are the same ones that stopsfacultative lagoons. The use of the aeradores can be intermittent.36c. Both first types of aeradas lagoons before mentioned, canto be followed of designed facultative lagoons with the purpose of treatingthe efluente of the primary lagoon, assimilating a great amount of solidsin suspension.d. For the design of aeradas lagoons of complete mixture they will be observedfollowing recommendations:_ the criteria of design for the process (kinetic coefficient ofdegradation, constant of autooxidación and oxygen requirements stopsyntheses) must ideally be determined throughexperimentation._ Alternatively will determine the proportions the lagoon aerada for the efficiencyof soluble removal of established DBO in conditions of the month morecold and with a constant of degradation around 0.025 (1/(mg/lXv.d)) to 20ºC, in where Xv are the volatile solid concentrationassets in the lagoon._ the oxygen requirements of the process (for synthesis and breathingendogenous) it will be determined for conditions of the hottest month.These will be corrected to conditions standard, by temperature andelevation, according to indicated in numeral 5.5.3.1 item 6._ will select the type of more advisable aerador, preferring itselfsuperficial mechanical aereadores, in agreement with hischaracteristics, speed of rotation, yield and cost. capacity of required and installed energy will be determinedselecting an even number of aeradores of equal size andspecified efficiencies._ For the removal of coliformes will be used the same coefficient ofnet mortality that the specified one for the facultative lagoons. quality of the efluente will be determined more for the conditions of the monthcold. For the effect the factor of dispersion will be able to be determined byaverage of the following relation:d = 2881 xs PRL2In where:PR is the expressed period of nominal retention in hours and L islength between the entrance and the exit in meters.In case of being used another correlation it will have to be justified beforecompetent authority.375.5.2.4 Facultative Lagoonsa. Its location like unit of treatment in a system of lagoonsit can be:_ As lagoon only (case of cold climates in which the load ofdesign is so low that it allows a suitable removal of bacteria)or followed of a secondary or tertiary lagoon (normally referredlike maturation lagoon), and_ Like a secondary unit after anaerobic lagoons oraeradas to process its efluentes to a greater degree.b. The criteria of design referred to temperatures and mortality of bacteriathey are due to determine in experimental form. Alternatively and whenthe experimentation is not possible, will be able to be used the following criteria:_ the temperature of design will be the average of the coldest month(temperature of the water), determined through correlations oftemperatures of the existing air and water._ In case of not existing those data, will determine the temperature ofwater adding to the temperature of the air a value that will be justifiedproperly before the competent organism, the same one that dependsof the meteorological conditions of the place._ In where it does not exist no data will be used the temperature average ofair of the coldest month._ the coefficient of bacterial mortality (net) will be adopted betweeninterval from 0.6 to 1.0 (l/d) for 20ºC.c. The load of design for facultative lagoons is determined withfollowing expression:CD = 250 xs 1.05 (T – 20)In where:CD is the surface loading of design in kg DBO/(ha.d)T is the temperature of the water average of the coldest month in ºC.d. Alternatively it can be used other correlations that will have to bejustified before the competent authority.e. The designer will have to adopt a load of smaller design todetermined previously, if factors exist like:_ the existence of abrupt variations of temperature,_ the form of the lagoon (the lagoons of extended form is sensible avariations and must have minors loads),38_ the existence of industrial remainders,_ the type of sewage system system, etc.f. In order to at heart avoid the growth of aquatic plants with roots,depth of the lagoons must be greater of 1.5 ms. For the design ofprimary a facultative lagoon, the designer will have to provide a heightadditional for the mud accumulation between periods of cleaning of 5 a10 years.g. For primary facultative lagoons the volume is due to determine ofaccumulated mud considering a 80% of solid removal insuspension in the efluente, with a reduction of 50% of volatile solidsby anaerobic digestion, a density of the 1.05 mud kg/l andcontent of solids from 15% to 20% to the weight. With these data it mustto determine the frequency of removal of mud in the installation.h. For the design of facultative lagoons that receive the efluente of lagoonsaeradas the following recommendations are due to consider:_ the oxygen balance of the lagoon must be positive, having init counts the following components:• the oxygen production by photosynthesis,• the superficial reaeración,• the assimilation of volatile solids of the affluent,• the assimilation of the soluble DBO,• the consumption by solubilización of solids in the digestion, and• the net consumption of I oxygenate of anaerobic solids._ is due to determine the volume of accumulated mud fromsolid concentration in suspension in the efluente of the lagoonaereada, with a reduction of 50% of volatile solids by digestionanaerobic, a density of the 1.03 mud kg/l and a content ofsolids 10% to the weight. With these data one is due to determinefrequency of removal of mud in the installation.i. In the calculation of removal of the organic matter (DBO) it will be possible to be usedany methodology properly sustained, with indication ofit forms in which the DBO concentration is determined (total or soluble).In the use of correlations of load of DBO applied to removed DBO,one is due to consider that the removed load of DBO is the differencebetween the total DBO of the affluent and the soluble DBO of the efluente. It stopslagoons in series are due to take in consideration that in the lagoonprimary the greater removal of organic matter takes place. concentration of DBO in the following lagoons is not predictable, hadto the influence of the populations of seaweed of each unit.395.5.2.5 Design of Lagoons for Removal of Pathogenic Organismsa. The dispositions that are detailed apply for any type oflagoons (in individual form or for lagoons in series), sincebacterial mortality and removal of parasites it happens in allunits and not only in the maturation lagoons.b. In relation to the parasites of residual waters, the nematodesintestinal they are considered like indicators, so that its removalit implies the removal of other types of parasites. For a suitable oneremoval of intestinal nematodes in a system of lagoon is requireda period of nominal retention of 10 days like minimum in one ofunits.c. The reduction of bacteria in any type of lagoons must, inpossible, to be determined in terms of fecales coliformes, likeindicators. For such effect, the designer must use the flow modeldispersed with the net coefficients of mortality for the different typesof units. The use of the model of complete mixture with coefficientsglobal of mortality he is not acceptable for the design of the lagoons inseries.d. The factor of dispersion in the model of dispersed flow can be determinedaccording to the form of the lagoon and the value of the temperature. The designerhe will have to justify the used correlation.The following values are referential for wide the long relation /:Long relation - wide Factor of dispersion d1 1,002 0,504 0,258 0,12e. The net coefficient of mortality can be corrected with the following onerelation of dependency of the temperature.KT = K20 x 1.05 (T - 20)In where:KT is the net coefficient of mortality to the temperature of water Taverage of the coldest month, in ºCK20 is the net coefficient of mortality to 20 ºC.405.5.2.6 General norms for the design of systems of lagoonsa. The period of design of the treatment plant must be included/understoodbetween 20 and 30 years, with stages of implementation of around 10years.b. In the conception of the project the following ones are due to followconsiderations:_ the design must be conceived at least with two units in parallelin order to allow the operation of one of the units during the cleaning._ the conformation of units, geometry, forms and number of cellsit must be chosen based on the topography of the site, and in individual ofan optimal earthwork, is to say of a suitable balancebetween the stuffed cut and for the docks._ the form of the lagoons depends on the type of each one ofunits. For the anaerobic and aeradas lagoons they are recommendedsquare or slightly rectangular forms. For the lagoonsfacultative one recommends extended forms; it is suggestedminimum long-wide relation is of 2._ In general, the type of entrance must not very be simplest possible andmoved away of the edge of the slopes, having to project with unloadingon the surface._ In the exit is due to install a device of measurement of volume(garbage dump or measurer of regime I criticize), with the purpose of being ableto evaluate the operation of the unit._ Before the exit of the primary lagoons is recommendedinstallation of a screen for the retention of creams._ the interconnection between the lagoons can take place by means of usingsimple pipes after the garbage dump or channels with a measurer ofcritical regime. This last alternative is the one of smaller loss ofload and of utility in flat lands._ the corners of the docks must be well-off to diminishaccumulation of creams._ the wide one of the berm on the docks must be at least of 2.5 msin order to allow the circulation of vehicles. In the primary lagoonswide it must so be that it allows the circulation of heavy equipment, as muchin the stage of construction like during the mud removal._ does not recommend the design of pipes, valves, floodgatesmetallic of drained of the lagoons because they are deteriorated bylack of use. For the drained one of the lagoons it is recommended41temporary installation of siphons or another alternative system of lowcost.c. The recommended free edge for the stabilization lagoons is of 0,5m. For the case in which surge by the action can be produced ofwind will be due to calculate a greater height and to design the protectioncorresponding to avoid the process of erosion of the docks.d. The operation of the lagoons is due to verify in the design stopsthe following special conditions:- During the conditions of putting in initial operation, the balancehydric of the lagoon (affluent - evaporation - efluente infiltration >)it must be positive during the first months of operation.- During the periods of cleaning, the applied surface loading onthe lagoons in operation do not have to exceed the fully factored loadcorresponding to the temperatures of the period of cleaning.e. For the design of the docks one is due to consider the following onesdispositions:_ is due to carry out the number of drillings necessary to determinethe type of ground and the layers to cut itself in the earthwork.In this stage the tests of ground mechanics will take place thatthey are required (the permeability in the site is due to include) foradapted design of the docks and forms of waterproofing. It stopsto determine the number of test pits will be had in considerationtopography and geology of the land, being observed like minimumfollowing criteria:• The minimum number of test pits is of 4 by hectare.• For the systems of several cells the minimum number of test pitsit will be determined by the number of cuts of the axes of the docksplus a perforation in the center of each one unit. For landsof rough topography in which pronounced cuts are requiredthe drillings will be increased when they are necessary.• The docks must be designed verifying that do not take placevolcamiento and that exists stability in the conditions moreunfavorable of operation, including drained fast and an earthquake.• The subpressures in the outer sides are due to calculate ofslopes to verify if the outer slope of the docks isadapted and to determine the necessity of controls like:waterproofing, coverings or filters of drainage.• In general the inner slopes of the docks must have oneinclination between 1:1,5 and 1:2. The outer slopes are lessinclined, between 1:2 and 1:3 (vertical one: horizontal).• Of the data of the drillings the type of material a is due to specifyto be used in the compaction of the docks and castrates ofwaterproofing, determining itself in addition the quarries todifferent materials that are required.42• The vertical interval of relief of the bottom of the lagoons and the phreatic levelit will have to be determined considering the constructive restrictions and ofcontamination of underground waters according tovulnerability of the water-bearing one.One will be due to design, if outside necessary, the system ofwaterproofing of the bottom and slopes, having to justify the solutionadopted.f. The following facilities are due to consider additional:_ House of the operator and equipment depot and tools._ Laboratory of residual water analysis for the control oftreatment processes, for cities with more than 75000 inhabitantsand others of so large minor that the competent organism considersnecessary._ For the aeradas lagoons is due to consider additionallyconstruction of an operation house, with area of office, factory andspace for the mechanical-electrical controls, in which it mustto settle a board of operation of the motors and other controlsthat they are necessary._ basic a weather station that allows the measurement ofenvironmental temperature, direction and speed of wind, precipitation andevaporation._ For the aeradas lagoons is due to consider the illumination and to assurethe supplying of energy in continuous form. For the effectit must study the convenience of installing a generator set._ the system of lagoons must be protected against damages by effect ofrun-off, designing itself roadside ditches of rainwater interceptionin case that the topography of the land therefore requires it._ the plant must count on perimetric wall of protection and signboardsadapted.5.5.3 Treatment with Activated Muds5.5.3.1 General aspectsto Next common aspects of the process are norman as muchconventional with muds activated like of all its variations.b. For effects of the present norms they are considered like optionsthose that have an efficiency of removal from 75 to 95% of the DBO.Between the possible variations the ventilation will be able to be selectedprolonged by oxidation ditches, in reason to his low cost. selection of the type of process will be justified by means of a technical studyeconomic, the one that will consider at least the following aspects:_ quality of the efluente;_ requirements and costs of preliminary and primary treatments;_ requirements and costs of ventilation tanks and sedimentadores43secondary;_ requirements and costs of the land for the facilities (includesunits of treatment of residual water and free mud, areas, etc.);_ cost of the mud treatment, including the amount of generated mudin each one of the processes;_ cost and life utility of the equipment of the plant;_ operational costs of each alternative (including the monitoreo ofcontrol of the processes and the quality of the efluentes);_ difficulty of the operation and described requirement of personnel.c. For the design of any variant of the activated mud process,they will have in consideration the following general dispositions:_ the fundamental criteria of the process like: age of mud,oxygen requirements, mud production, efficiency and density ofbiomass must be determined in experimental form according tothe indicated thing in article 4.4.4._ In where he is not requisite to develop these studies, will be able to be useddesign criteria._ to determine the efficiency is considered to the mud processactivated jointly with the secondary or efluente sedimentadorseparated liquid of the biomass._ the design of the ventilation tank takes place for the conditions ofof great volume means. The process will have to be in capacity to givequality established for the efluente in the conditions of the month morecold.d. For the ventilation tank one will verify the values of the following onesparameters:_ period of retention in hours;_ age of muds in days;_ volumetric load in kg DBO/m3;_ removal of DBO in %;_ volatile solid concentration in suspension in the tank ofventilation (SSVTA), in kg SSVTA/m3 (this parameter alsoit knows like volatile solids in suspension of the mixed licor -SSVLM);_ load of the mass in kg DBO/Kg SSVTA. day;_ rate of recirculation or rate of return in %.e. In case of not requiring the tratabilidad tests, they will be able to be usedfollowing referential values:44TYPE OFPROCESSPERIOD OFRETENTION(h)AGE OFMUD(d)LOADVOLUMETRICkg (DBO/m3.día)Conventional 4 - 8 4 -15 0.3 - 0,6Ventilationstaggered3 - 6 5 -15 0.6 - 0,9High load 2 - 4 2 - 4 1.1 - 3,0Ventilationprolonged16 - 48 20 - 60 0.2 - 0,3Mixture completes 3 - 5 5 - 15 0.8 - 2,0Ditch of oxidation 20 - 36 30 - 40 0.2 - 0,3Additionally one will be due to have in consideration the following parameters:TYPE OFPROCESSRemovalof DBOConcentracióSSTA nkg/m3Load ofmass kgDBO/ (kgSSVTA.día)Rate ofrecirculación %Conventional 85 - 90 1.5 - 3.0 0.20 - 0.40 25 - 50Ventilationstaggered85 - 95 2.0 - 3.5 0.20 - 0.40 25 - 75High load 75 - 90 4.0 - 10 0.40 – 1,50 30 - 500Ventilationprolonged75 - 95 3.0 - 6.0 0.05 – 0,50 75 - 300Mixture completes 85 - 95 3.0 - 6.0 0.20 – 0,60 25 - 100It settles ofoxidation75 - 95 3.0 - 6.0 0.05 – 0,15 75 - 300NOTE: The selection of another process will have to be justified properly.f. For the determination of the capacity of oxigenación of the processthey will have to consider the following dispositions:_ the oxygen requirements of the process must calculate forconditions of operation of temperature monthly average more dischargeand they must be sufficient to supply oxygen for the synthesis oforganic matter (DBO removal), for the endogenous breathing andfor the nitrificación._ These requirements are given in conditions of field and must becorrected to conditions standard of zero percent of saturation,standard temperature of 20 ºC and one atmosphere of pressure, with the useof the following relations:N20 = NC/FF = and x Q T - 20 (CSC x ß - Ci)/9,0245CSC = CS (P - p)/(760 - p)p = exp (1.52673 + 0.07174 T - 0.000246 T 2)P = 760 exp (- and/8005)CS = 14.652 - 0.41022 T + 0.007991 T 2 - 0.000077774 T3In where:N20 = requisite of oxygen in standard conditions, kg O2/dRequisite NC = of oxygen in conditions of field, kg O2/dF = correction factorAnd = correction factor that relates the coefficients ofoxygen transference of the remainder and the water. Its valueproperly it will be justified according to the type of ventilation.Generally this value is in the rank of 0.8 a0,9.Q = factor of temperature dependency whose value is takenlike 1.02 for compressed air and 1.024 by ventilationmechanics.CSC = concentration of oxygen saturation in conditions offield (P pressure and temperature T).ß = correction factor that relates the concentrations ofsaturation of the remainder and the water (in conditions offield). Its value properly will be justified according totype of ventilation system. Normally it is assumedvalue of 0.95 for the mechanical ventilation.Ci = oxygen level in the ventilation tank. Normallyit is assumed between 1 and 2 mg/l. Under no circumstance ofoperation will allow a smaller oxygen level of 0,5mg/l.CS = concentration of oxygen saturation in conditions tolevel of the sea and temperature T.P = atmospheric Pressure of field (to the elevation of the place),mm Hg.p = steam pressure of the water to the temperature T, mm Hg.And = Elevation of the site in meters on the level of the sea._ the use of other relations must be justified properly beforecompetent organism._ the correction to standard conditions for the ventilation systemswith compressed air he will be similar to the previous thing, but in addition it must havein account the characteristics of the diffuser, the air flow anddimensions of the tank.46g. The selection of the type of aereador will have to be justified properly technicaland economically.h. For the systems of mechanical ventilation the following ones will be observeddispositions:_ the installed capacity of energy for the ventilation will be determinedrelating the oxygen requirements of the process (kg O2/d) andyield of the selected aereador (kg O2/Kwh) both inconditions standard, with the respective correction by efficiency inmotor and reducer. The number of ventilation equipment will be likeminimum two and preferredly of equal capacity consideringthe standardized capacities of manufacture._ the yield of the aereadores must be determined in a tank withclean water and a density of energy between 30 and 50 W/m3. yields will have to be expressed in kg O2/Kwh and the following onesconditions:_ a pressure atmosphere;_ zero percent of saturation;_ temperature of 20 ºC._ the motor-reducing set must be selected for a regime ofoperation of 24 hours. A factor is recommended on watch of1,0 for the motor._ the installed capacity of the equipment will be previously determined,but without the efficiencies of the motor and reducer of speed._ the ventilation rotor must be of stainless steel or another materialresistant to the corrosion and approved by the competent authority._ the density of energy (W/m3) will be determined relatingcapacity of the equipment with the volume of each tank of ventilation. density of energy must allow a speed of circulation ofmixed licor, so that the sedimentation does not take place ofsolids._ the location of the aeradores must so be that an interaction existsof its areas of influence.i. For systems with compressed air diffusion it will be come in formsimilar, but considering the following factors:- the type of diffuser (fine or heavy bubble);- the constants characteristic of each diffuser;- the yield of each unit of ventilation;- the air flow in standard conditions;- the location of the diffuser with respect to the depth of the liquid, and47wide of the tank.- altitude above sea level.The required power will be determined considering the load ondiffuser plus the pressure drop by the flow of the air throughpipes and accessories. The design capacity will be 1.2 timesnominal capacity.