Determination of Biosolids Phosphorus Content and Solubility and Their Relationships with Water Resource Recovery Processes

Transcription

1 Determination of Biosolids Phosphorus Content and Solubility and Their Relationships with Water Resource Recovery Processes Dr. Jeff White Department of Crop and Soil Sciences North Carolina State University

2 Regulating Land Application of Biosolids : Protecting Water/Soil Quality and Human/Animal Health Primary EPA 503 standards for land application limit: Potentially toxic metals: As, Cd, Cr, Cu, Pb, Hg, (Mo), Ni, Se, Zn Cu, Mo, Ni, Zn are essential plant micronutrients Pathogens: worms, parasites, bacteria, viruses, etc. Disease vector attractants: rodents, flies, wildlife, etc. Permits required for most land application biosolids class/quality receiving field characteristics dwelling setbacks, stream buffers, slope, soil characteristics, receiving history, etc... Permitting authority ceded to states: NC DEQ State regulations must meet 503 but may be stricter Subsequent standards for land application are governed by: Plant available nitrogen (N) of biosolids Agronomic N needs of the crop and soil

3 Problems with N-Based Rates: Increase P-loss Risk Crops N:P 3:1 to 8:1 Biosolids N:P 1:1 to 1:2 Applying on N basis will surpass crop P needs Example Assume crop N:P = 5:1 Assume biosolids N:P = 1:2 If crop needs/removes 130 lb N/ac = 26 lb P /ac Applied on N basis: 130 lbs N/ac = 260 lbs P/ac Excess P = 234 lb/ac inefficient input use and economics increased loss to ground & surface water

4 Eutrophication P moves dissolved in runoff and attached to soil particles Fertilizes low-p surface waters Death of aquatic species Decomposed by microbes Algae blooms & excess aquatic vegetation Microbial respiration uses up dissolved O 2

5 Nutrient Application Based on P-Loss Risk Currently, no NC regulations re biosolids P USDA-NRCS Nutrient Management Standards 4 R s: right form, right amount, right time, right place Standards must be met if grower has: nutrient management plan by USDA-NRCS or Soil and Water Conservation District state or federal agricultural cost share $$$ animal waste regulated under NC 02 / NPDES permits nutrient sensitive Neuse or Tar-Pamlico River Basins. If P > agronomic rate: must determine P loss risk NC: Phosphorus Loss Assessment Tool (NCPLAT)

6 NC PLAT: Assessing P-Loss Risk at Field Level Four loss pathways estimated: Soil-attached P via erosion Soluble soil P via runoff Soluble soil P via leaching Applied P loss: animal waste / fertilizer rate and application method P concentration (total P), water-soluble fraction Research-based book values for manures & fertilizers

7 NC PLAT: Assessing P-Loss Risk at Field Level Four loss pathways estimated: Soil-attached P via erosion Soluble soil P via runoff Soluble soil P via leaching Applied P loss: animal waste / fertilizer rate and application method P concentration (total P), water-soluble fraction Research-based book values for biosolids?

8 Research Objectives Determine the total and soluble P content of NC biosolids: Sample and analyze biosolids from WRRF Determine if relationships exist between water resource recovery processes and biosolids P fractions Survey WRRF to document treatment processes Develop biosolids categories linking processes to P fractions: book values Implement in PLAT to assess bisolids P-loss risk

9 Materials and Methods

10 Processes & Chemicals Affecting Biosolids P Biological Activated sludge: anaerobic and aerobic zones allow microbial P accumulation Chemical P precipitates: metal salts, alkalizing chemicals Physical Dewatering techniques Major influences on: consistence P content & solubility pathogen reduction

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12 Survey Development Created an online survey using Qualtrics ( Survey asked questions about WWTP processes

13 Survey Distribution Large Municipal Discharge Sites ~100 LMDS in NC: Info from NCDEQ ed flowchart and survey to the Operators in Responsible Charge ~40% survey response rate To qualify for further study: Land apply Provide final product Willing to participate 26 WRRF

14 Biosolids P and Dry Matter Analysis Seasonality? sampled Summer, Fall, and Winter 28 biosolids from the 26 WRRF Determine: Dry matter content (DM) Oven drying Total P (TP) Dry ash acid digestion and ICP-OES Water-extractable P (WEP) Water extraction and ICP-OES Quantify: Soluble P fraction Soluble P fraction = WEP/TP Percent WEP = (WEP/TP)*100

15 Results

16 Total P Seasonal Variability Dry Matter WEP PWEP

17 Why More Total P in Winter? Many factors influence microbial populations in WRRF Temperature Precipitation Literature contradictory de-bashan et al. (2004 less biological P removal at low temperatures: microbial strains grew well at 15 C, but limited at 5 C Water Environment Federation (2006) greater biological P removal at low temperatures: P-accumulating organisms (PAO) selective low temperature outcompete competitors for substrate accumulation

18 Frequency Distributions: Averaged over Seasons Mean: 1.4 g kg -1 = 0.14% Right skewed Mean: 1.4 g kg -1 = 0.14% Median: 0.6 g kg -1 = 0.06% Large range: %

19 Frequency Distributions

20 Correlations Among Parameters? Estimate PWEP based on WEP No need to measure Total P?

21 Cluster Analysis to Group WRRF by Treatment Processes: No Relationships to P

22 Regulated Biosolids Classes Two biosolids classes: Class B and Class A Differed by solids processing stabilization methods to reduce heavy metals, pathogens, and vector attractants Class B: Treated with a Process to Significantly Reduce Pathogens (PSRP) Typically stabilized by anaerobic and aerobic digestion Slurries and cakes Class A: Treated with a Process to Further Reduce Pathogens (PFRPs) More stringent processes Dry cakes and pellets

23 Surveyed/Sampled Class B Biosolids 71% of biosolids were Class B To meet PSRPs: Majority slurries digested aerobically Majority cakes digested anaerobically But some exceptions Biggest difference? Consistency Gap between 6.3 and 12.6% solids Slurries: 1.4 to 6.3% Cakes: 12.6 to 24.3%

24 Surveyed/Sampled Class A Biosolids 29% of the biosolids were Class A Pathogen reduction: either heat dried or alkaline stabilized Thermal heat drying: Water evaporated from solids Converts soluble P to nonsoluble P Slows rates of decomposition in soil Alkaline stabilization: Typically treated with lime kiln dust (LKD) CaO and MgO High heat and high ph Requirements: ph >12 for >72 hours, >52 C >12 hours Land application Overdosing common if lime value not considered P highly diluted Used as soil liming agent Ca/Mg-Phosphates decrease solubility temporarily Soil acidity solubilizes P over time

25 Biosolids Types for NCPLAT Class A: separated by processes to further reduce pathogens (PFRP) Class B: separated by consistency Established four biosolids types: o Class A alkaline stabilized o Class A thermally heat dried o Class B slurries o Class B cakes

26 Biosolids Categories: Values for PLAT Alkaline: lower TP on dry mass/mass basis dilution by lime very low WEP, PWEP: formation of Ca/Mg-phosphates makes P less soluble in short term Heat dried, slurry, cake: ~ same TP (dry weight basis) Heat dried: intermediate WEP and PWEP drying converts some P into insoluble forms Cake (vs. slurry): lower PWEP most soluble P leaves in filtrate/centrate/pressate

27 PLAT Application Rates PLAT involves practical land application rates Instead of dry weight g P /kg biosolids, need to convert to actual application rates as land applied As is weight basis: Class B slurries: lbs P per 1000 gal (by volume) Class B cakes, Class A alkaline, and Class A heat dried: lbs P / ton (by mass)

28 NC PLAT Coefficients in Application Units Biosolids Type Units: Pounds P Per Total P Soluble P Fraction Soluble P Nonsoluble P Class A alkaline ton Class A heat dried ton Class B cake ton Class B slurry 1000 gal Bad News: No $$$ to re-program NCPLAT to incorporate these coefficients

29 Good News! Compared to animal wastes: biosolids WEP and PWEP relatively low WEP Biosolids: g/kg; mean = 1.4 g/kg Representative animal wastes in NC PLAT PWEP 3.0 g/kg for turkey house litter 24.7 g/kg for swine lagoon effluent Biosolids: 0.2 to 35%; mean = 5% Animal wastes in NC PLAT 25% for poultry wastes 80% for a variety of animal waste lagoon liquids Land application of NC biosolids presents little P- loss risk relative to animal wastes

30 WRRF Reducing Biosolids P: Recovery Precipitation and harvest of struvite from WRRF liquid streams NH 4 MgPO 4 6 H 2 O N-P-K = Uses slow release fertilizer animal feed Advantages for WRRF (No brand endorsement implied!) Generate revenue (although large initial investment) Decrease effluent P loads Decrease biosolids N:P? Less reliance on treatment methods for nutrient reduction

31 Thanks to: NCSU Molly Jameson, M.S. Dr. Deanna Osmond Dr. Tarek Aziz Robert Walters, Research Specialist Robert Dodson, former Superintendent: Durham WRRF NCDEQ: Chonticha McDaniel Ed Hardee Mike Templeton All cooperating WRRF personnel, especially: Jean Creech / Charlotte Tim Woody / Raleigh WWW: many graphics

32 More Information Jameson, M., J.G. White, D.L. Osmond, and T. Aziz Determination of Biosolids Phosphorus Solubility and Its Relationship to Wastewater Treatment. Water Environment Research 88 (7): ( NCPLAT: now combined with Nitrogen Loss Estimation Worksheet in the NC Nutrient Assessment Tool NC Realistic Yield Expectations (RYE) database NCDA&CS Waste & Compost Analysis Guide

33 Questions?