Solids Content and Stability of Air-Dried Biosolids Stored in Stockpiles

Transcription

1 Solids Content and Stability of Air-Dried Biosolids Stored in Stockpiles Wale Oladeji, Guanglong Tian, Albert Cox, Dan Collins Metropolitan Water Reclamation District of Greater Chicago

2 Biosolids ~ 8 million DT produced nationally each year: > 95% reused beneficially MWRD generates ~180,000 DT of biosolids annually Fertilizer on farmland (60%) Controlled Solids Distribution (CSD) Soil substitute on landfill

3 Controlled Solids Distribution (CSD) Air dried biosolids - for local users Economical Beneficial to local community Support Chicago s green initiative Applying dried biosolids on turf

4 CSD Biosolids Uses Golf courses Parks Athletic fields Landscaping Construction companies

5 Air Dried Biosolids Challenges Availability when needed Storagability - odor Limit acceptability can cause opposition despite benefits Impact cost effectiveness of CSD biosolids

6 Sources of Odor in Air-Dried Biosolids Stored biosolids odors due to: Biological degradation - anaerobic conditions Sulfur and N compounds Others - volatile fatty acids, esters, alcohols, aldehydes, ketones, phenols, others Compounds Characteristic Odor Formula Odor Detection Thresholds (ppm) Hydrogen sulfide Rotten eggs H 2 S Methyl mercapton Decayed cabbage CH 3 SH Dimethyl sulfide Decayed vegetables CH 3 SCH Dimethyl disulfide Unpleasant CH 3 SSCH Ammonia Sharp pungent NH Trimethyl amine Fishy N(CH 3 )

7 Air-Dried Biosolids and Odor Development Odor associated with a wide range of compounds Difficult to control odor by any single approach Residual moisture (20 40%) increase odor potential?

8 Air-Dried Biosolids and Odor Development Microbial activities affected by: Constituents (C, N, S, microbes) Solids content ph Others

9 Stabilizing Biosolids Biological Digestion Composting Aeration Heat Drying Pelletization Alkaline stabilization Air dry to stable solid Content?????

10 Range of solids content in biosolids distributed by under CSD program during Dried Biosolids Solids Contents MWRD biosolids can be air dried to 52 95% solids.

11 Hypothesis There is a critical moisture level at which biosolids can be stored with minimal potential for odor emissions.

12 Method Biosolids: Anaerobically digested, centrifuged, dewatered, and aged Dried to target 55, 60, 65, 70, 75, & 80% solid contents 40 cubic yards each stockpiled to ~ 5 ft depth 5 ft 55% 60% 65% 70% 75% 80% Drying to obtain six different solid contents

13 Samplings and Analysis Sampling Biweekly for 2 months, then at 8 and 12 months At 30 40cm depth Analysis Odor (ED50) - adapted from Lordi et al., 2002 Temperature ph TKN NO3-N NH4-N Solids content

14 Odor Analysis Odor analysis done by ED50 using Olfactometer IIT Research Institute Dynamic Forced-Choice Triangle Olfactometer

15 Temperature Temperature Trend of temperature similar irrespective of solid content increased from < 40 0 C to ~ 65 0 C and then decreased to < 30 0 C The stockpiles were all microbially active % Solids 60% Solids 65% Solids 70% Solids 75% Solids 80% Solids 2-May Aug Nov Feb-11 6-Jun Sep-11 Sampling Date

16 Solid Contents Measured solids content generally higher than targeted Solid content became similar over time Treatment Time Zero (%) After 1 Year (%) T1 (55% Solids) T2 (60% Solids) T3 (65% Solids) T4 (70% Solids) T5 (75% Solids) T6 (80% Solids) 77 79

17 ED50 Odor The six piles show: increased odor within the first 15 days odor decreased thereafter Greatest odor in Pile 1-55% solids after15 days % Solids 60% Solids 65% Solids 70% Solids 75% Solids 80% Solids Days After Stockpiling

18 Nitrogen TKN show minimal changes Transformation - Denitrification Minimal N loss Biosolids NH 3 -N increased with time NO 3 -N decreased with time but increased afterward

19 Summary Impacts of solids contents on biosolids stability may be minimal when biosolids with solid content > 60% is stockpiled. Stockpiled dried biosolids will show initial odor increase due to microbial activity, but the odor will dissipate with time Minimal N losses and N transformation

20 Thanks Wale Oladeji MWRDGC Monitoring and Research Department