Reactive Phosphorus Removal fromAquaculture and Poultry ProductionsSystems Using Polymeric HydrogelsPETER KOFINAS* ANDDIMITRI R. KIOUSSISDepartment of Chemical Engineering, University of Maryland,College Park, Maryland 20742-2111This work reports on the features of a sorption processesfor the ultimate removal and recovery of reactive phos-phorusfromaquacultureandpoultryproductionwastewatereffluents. The sorbent used was a cross-linked polyamine(PAA‚HCl) polymeric hydrogel. ThePAA‚HCl hydrogels wereprepared by chemically cross-linking aqueous solutionsof linear PAA‚HCl chains with epichlorohydrin (EPI). Thephosphorus binding capacity of the gels was measured instandard aqueous solutions as a function of ionic strength.Equilibrium PO43-, loadings of 100 mg anion/g gel wereobtained. The regeneration ability of the gels wasdemonstrated by release of the bound phosphorus anionsupon washing with 1-2 M NaOH solution, providingopportunities to recover and reuse the gel over multiplecycles. The ionic polyamine gels have been demonstratedto be appropriate materials for treating poultry andaquaculture wastewater effluents. Upon treatment,phosphorus anion concentrations were reduced to levelssuitable for discharge into natural surface waters.IntroductionAquatic ecosystems are often limited in the availability oftwo nutrients: phosphorus (P) and nitrogen (N) (1-4).Limited nutrient availability prevents the excessive growthofalgaebloomsthatproduceunsightlyareas,lowersdissolvedoxygen (DO) concentrations in the water, and may lead tofish kills (1). Methods that will effectively remove nutrientanion pollutantseven atextremely lowconcentrations fromwastewater effluents are a major environmental need. Thiswork describes an approach that introduces novel cross-linked cationic polymeric materials into the contaminatedaqueous slurry. The polymer materials we have developedselectivelybindthepollutantanionsintothepolymermatrix,permittingtheirsubsequentremovalfromthecontaminatedsystem. The polymer containing the bound pollutant anioncaneitherberegeneratedorincinerated.Thetreatedsystemcan then be safely discharged intonatural waters or sent forfurther treatment for use as a municipal water supply.Pfiesteriaoutbreakshaveoccurredinestuarinewaterwaysfrom Delaware and Maryland to North Carolina. Pfiesteria,atoxic organism,attacksandkillsfish inamatterofminutes(1). This organism has also been shown to affect humans.Symptoms range from skin rashes, to respiratory problems,and memory loss. The vast majority of outbreaks haveoccurredin waterwaysthathavehighnutrientlevels. ItisforthesereasonsthatrecentlytheWaterEnvironmentResearchFoundation (WERF) prepared a detailed report that over-viewed the present state of technology and identified highpriority research needs pertaining to nutrient removal (5).Aquacultureisarapidlyexpandingindustrythatrequiresquantities of water in the order of 200-600 m3per kg fishproduced(6).Manyaquacultureproductionfacilitiesoperateas “flow through” or “open” systems thus releasing largequantitiesof nutrientrichwaterintoanother receivingbodyof water. At sufficiently high concentration levels, nutrientanions can become toxic to fish or lead to the crash of aphytoplankton bloom resulting in the rapid growth offilamentous algae or undesirable macrophytes (6-8). Pro-ductivity is the most conspicuous aspect of cultural eutroph-ication.Itisacceleratedbytherunofffromaquaculturewastedischarges, rich in nutrients.Poultry litter, also referred to as broiler litter as it isgeneratedprimarily inbroilerproduction,hasrecentlybeenthe focus of attention as a source of excessive phosphorus(P)levelsinagriculturalsoilstowhichitisappliedasfertilizer.The litter is removed from chicken houses in the form of adry cake and is stored in piles either under a roof or in theopenorisspread directlyontothefarmfieldsinitsdry form.Poultry litter has a nitrogen (N) content of 2-4 wt % and iscommonly applied to farm fields as a N source for crops.Broiler litter contains up to 4% P, which is far in excess ofthe crop P requirement (most plants require: 0.05-1.0% P)(9, 10). Broiler litter is usually removed from the houses ata frequency often less than once per year. It contains theaccumulated components of chicken excrement. 1/4 of thetotal N produced is lost in the form of ammonia (NH3) dueto continuous vaporization over the life of the litter (9). Ptends to accumulate because it cannot assume a volatileform. Excess P and N applied to the soil may cause nutrientrunoff and potential contamination to surface and ground-water sources. Nutrient management regulations haverecentlybeenissuedwhichwillrequirebroilerlitterandotherPcontainingmanurestonolongerbeappliedtofieldswhoseP levels exceed regulations.We have developed polyamine polymers which can becross-linkedtoformthree-dimensionalhydrophilicpolymernetworksthatareabletoabsorblargeamountsofwater. Theresulting water-swollen polymer network is prevented fromdissolving due to the presence of tie-points between thepolymerchains(i.e.,cross-links)andischaracterizedbyhighmechanicalstrength.Anionscanbeselectivelyandreversiblybound into the polymer matrixpermitting their subsequentremoval from the contaminated system. To be effective inremoving pollutant anions from wastewater effluents, therate of transport of the anions into the gels must be largeenough so that efficient binding can be achieved. Thetransport process must also be reasonablyinsensitive to pHchanges so that the anions can be bound from wastewatersof varying pH. Furthermore, the presence of particulates(suspended solids), organics, and counterions which arecommonfoulingconstituentsofwastewaters,shouldnotlimitthe anion removal ability of the gels.Materials and MethodsMaterials Used. Poly(allylamine) hydrochloride (PAA‚HCl)solidpowder(25g),sodiumhydroxide(NaOH)(pellets, 97%),sodiumnitrate(NaNO3)(99+ %),andsodiumnitrite(NaNO2)(97+%)werepurchasedfromAldrichChemicalCo.Thecross-linking agent purchased from Aldrich, epichlorohydrin 99+%solution (EPI),wasusedtoproduce thehydrogelnetwork.All reagents were ACS grade and were used without furtherpurification. The PhosVer3, NitraVer5, reagents used to* Corresponding author phone: (301)405-7335; fax: (301)405-0523; e-mail: [email protected]. Sci. Technol.2003,37,423-42710.1021/es025950u CCC: $25.00  2003 American Chemical Society VOL. 37, NO. 2, 2003 / ENVIRONMENTAL SCIENCE & TECHNOLOGY9423Published on Web 12/13/2002perform the UV-vis concentration