ASTM_E_1625_-_94_2001.pdf

Designation:E 1625 94(Reapproved 2001)Standard Test Method forDetermining Biodegradability of Organic Chemicals in Semi-Continuous Activated Sludge(SCAS)1This standard is issued under the fixed designation E 1625;the number immediately following the designation indicates the year oforiginal adoption or,in the case of revision,the year of last revision.A number in parentheses indicates the year of last reapproval.Asuperscript epsilon(e)indicates an editorial change since the last revision or reapproval.1.Scope1.1 This test method covers procedures for the determina-tion of the biodegradability or removability,or both,ofnonvolatile organic chemicals(Henrys Constant 103atm/m3/day);however,ithas been used for chemicals that are not completely volatilizedbetween additions to the SCAS system(5,7).For chemicals ofmoderate volatility,volatilization losses during a cycle may beevaluated by scrubbing of aeration off-gases through a solventtrain(usually three consecutive traps containing acetone,methylene chloride,or hexane)or polymeric trap(for example,Tenax10or SEP-PAK11).Specific chemical analysis of eachsolvent trap or polymeric trap is then carried out.8.2.7 Highly polar non-extractable test chemicals that areassociated with the mixed liquor solids require specializedtesting and analytical procedures that cannot be fully docu-mented in this test method,for example,use of14C-labeledmaterials and special apparatus.However,the basic SCASoperating system can be employed if appropriate mass balancescan be obtained.9.Procedure9.1 The activated sludge mixed liquor suspended solids(MLSS)are generally obtained from the treatment plant severalweeks prior to the start of the SCAS test.Source of MLSS iseither the aeration basin or return stream from the secondaryclarifier.9.2 Filter MLSS through a 20-mesh stainless steel screen toremove extraneous particulate matter and concentrated bysettling and decanting of supernate to a suspended solidscontent of 4000 to 6000 mg/L.This concentration is typicallyfound in the activated sludge return line from the secondaryclarifier.9.3 Mixed liquor suspended solids(MLSS)from 9.1(4000to 6000 mg/L)are then charged to a 10-L reservoir where theyare aerated prior to test initiation.Maintain the reservoir in thesame manner as the smaller SCAS test chambers using 24 and72-h weekend time cycles.At the end of the time-cycle,aeration is halted,solids are allowed to settle,and supernatedrained to one third of the original mixed liquor suspendedsolids volume.The reservoir is then charged with natural orsynthetic sewage to the original volume and aeration,at a rateto maintain vigorous agitation of MLSS,is resumed.Deter-mine stabilization of the activated sludge by monitoring DOCremoval until steady-state removal is achieved.9.4 When natural sewage(obtained either before or afterprimary clarification)is used to maintain the reservoir andSCAS units,it is obtained generally on a weekly basis from theDWTP.Filter the sewage through glass wool to remove largeparticulates and stored in a refrigerator at 5C until use.9.5 The SCAS units are charged with MLSS from thereservoir generally one week prior to the start of a test.9.5.1 The MLSS of the reservoir is determined on a weeklybasis using a 5-mL aliquot of the mixed liquor.Collect solidson a weighed glass-fiber filter contained in a Gooch crucibleand dry in an oven at 105C.9.5.2 Add sufficient MLSS to each SCAS unit so that theMLSS level is maintained in the 2000 to 3000-mg/Lrange.Usesynthetic or natural sewage for dilution,if necessary.9.5.3 Check the MLSS of the individual SCAS units usinga single 10 to 20-mLmixed liquor aliquot prior to initial dosingand on a once per week basis thereafter.The nutrient level ofthe natural sewage should also be checked on a weekly basis.If the MLSS level should fall below 2000 mg/L,the addition ofnon-acclimated MLSS from the reservoir may be advisable ifthe study is to continue for any extended period of time.IfMLSS concentrations builds to 4000 mg/L,remove activatedsludge to lower the concentration to the 2000 to 3000-mg/Lrange.9.6 Connect the SCAS units to a compressed air manifoldand aerate each unit at a flow rate sufficient to maintaindissolved oxygen(DO)levels of at least 2 mg/L(about 0.3mL/min/mL liquid).Reduced flow may be necessary forvolatile chemicals.Removal by way of volatility or adsorption,or both,can also be assessed in a separate SCAS unitmetabolically poisoned,for example,with 1%mercuric chlo-ride.Additional mixing for the 1500-mL SCAS units can be10Tenaxt,available from Alltech Association Inc.,2051 Waukegan Road,Deerfield,IL 60015-1899,has been found suitable for this purpose.11SEP-PAKt,available from Water Chemical Products Department,Milford,MA 01757,has been found suitable for this purpose.E 16254provided by magnetic stirring as shown in Fig.2.Maintaintemperature at 22 6 3C.9.7 The basic time cycle used in this test is 24 h(optional72-h cycle on weekends is permitted).9.7.1 At the beginning of each