Economical Approach to Treatment of Soluble and Particulate As, Cu, Zn, and Cr in Stormwater Runoff to Meet BCWQGs AW

Transcription

1 Economical Approach to Treatment of Soluble and Particulate As, Cu, Zn, and Cr in Stormwater Runoff to Meet BCWQGs AW Presented by Elena Ranyuk, PhD MBA October 12, 2017 RemTech 2017 Banff, AB 1

2 Overview Heavy metals pollutants & BCWQGs Our case study - Overview - Treatment method selection - Phase I: Co-precipitation with an Al coagulant - Phase II: Packed bed adsorption Key Learnings 2

3 Heavy Metals Pollutants Long-term BCWQGs for the Protection of Freshwater Aquatic Life (Approved & Working 2016) Cu 4 ppb As 5 ppb Zn 15 ppb Se 1 ppb Cr 1 ppb for Cr(VI) 8.9 ppb for Cr(III) Hardness dependent guidelines are calculated at 100 ppm calcium hardness; D: dissolved T: total Fe 1000 ppb for T 350 ppb for D Pb 6 ppb Mn 1045 ppb Cd 0.12 ppb for D Hg 0.01 when MeHg = 1.0% of THg Co 4 ppb Ni 96 ppb Ag 0.05 ppb Sn ppb (organotin comp.) 3

4 Our Case Study CLIENT: Medium size business in British Columbia Limited funds available INCOMING WATER PROFILE: Neutral ph Varying concentrations of soluble and particulate As, Zn, Cu, & Cr TREATMENT OBJECTIVE: Achieve BCWQGs for Protection of Freshwater Aquatic Life Must be economical 100 gpm (6.3 L/s) continuous flow treatment BCWQG H=100 Intake Dissolved Metals Cu 4 ppb ppb; average = 300 As 5 ppb ppb; average = 65 Zn 15 ppb ppb; average = 150 Cr 1/8.9 ppb ppb; average = 74 4

5 CHALLENGES Common Metal Removal Methods Cost Technical complexity Chemical Precipitation Ion Exchange Membrane Filtration Adsorption Different optimal conditions for different water profiles Fluctuations in water intake affect the outcome Periodic regeneration of IX resin required Mgmt. of liquid waste streams Pre-treatment required Generation of ~30% of reject is typical Other waste streams require mgmt. Comprehensive pretreatment required Different wastewater sources may require different adsorbents & EBCT Removal of TSS & optimal ph required 5

6 CHALLENGES Common Metal Removal Methods 1 2 Chemical Precipitation Ion Exchange Membrane Filtration Adsorption Different optimal conditions for different water profiles Fluctuations in water intake affect the outcome Periodic regeneration of IX resin required Mgmt. of liquid waste streams Pre-treatment required Generation of ~30% of reject is typical Other waste streams require mgmt. Comprehensive pretreatment required Different wastewater sources may require different adsorbents & EBCT Removal of TSS & optimal ph required 6

7 Phase 1: Chemical Precipitation Method Zn 2+ + NaOH ---> Na + + Zn(OH) 2 (s) Soluble zinc Zinc hydroxide Zn(OH) 2 Precipitate by A. Lambert Photography Colloidal metal precipitate Coagulate Flocculate Settle Clarify Effluent w/lower metal conc n 7

8 Concentration of dissolved metal (mg/l) Chemical Precipitation: Minimum Solubility 1000 ppb 100 ppb 10 ppb 1 ppb 0.1 ppb ph ph Theoretical solubilities of metal hydroxides as a function of ph Source: EPA 625/

9 Concentration of dissolved metal (mg/l) Chemical Precipitation: Minimum Solubility Zn 1000 ppb 100 ppb 10 ppb Minimum solubility 100 ppb BCWQG for Zn at H= ppb 1 ppb 0.1 ppb ph ph Theoretical solubilities of metal hydroxides as a function of ph Source: EPA 625/

10 Concentration of dissolved metal (mg/l) Chemical Precipitation: Minimum Solubility Cd 1000 ppb 100 ppb 10 ppb 1 ppb 0.1 ppb ph Theoretical solubilities of metal hydroxides as a function of ph ph Minimum solubility 1 ppb BCWQG for Cd 0.12 ppb Source: EPA 625/

11 Concentration of dissolved metal (mg/l) Chemical Precipitation: Minimum Solubility 1000 ppb Pb Minimum solubility 6000 ppb 100 ppb 10 ppb 1 ppb 0.1 ppb ph Theoretical solubilities of metal hydroxides as a function of ph ph BCWQG for Pb at H=100 6 ppb Source: EPA 625/

12 Concentration of dissolved metal (mg/l) Chemical Precipitation: Minimum Solubility 1000 ppb Cu 100 ppb 10 ppb 1 ppb 0.1 ppb ph Theoretical solubilities of metal hydroxides as a function of ph ph 4 ppb BCWQG for Cu at H=100 Minimum solubility 4 ppb Source: EPA 625/

13 Chemical Precipitation in Real Life In most cases, ACTUAL solubilities > THEORETICAL solubilities due to: Incomplete reactions Different optimal ph points for precipitation of different metals Poor separation of colloidal precipitates Formation of soluble metal-complexes with naturally occurring & androgenic chelates Hence, in practice, the GAP is likely to be even LARGER 13

14 Enhanced Metal Removal with Al/Fe Coagulants ACTUAL solubilities MAY be LOWERED due to co-precipitation & adsorption processes M 3+ + H 2 O M n (OH) m (H 2 O) x (3n-m) Amorphous floc of aluminum/iron(iii) hydroxide Cu, Zn, Cd are adsorbed best at high ph Oxyanions (AsO 4 3-, CrO 4-, SeO 3 2- ) are adsorbed best at low ph Process is focused on ph and coagulant dosages rather than on the solubilities of each metal 14

15 Phase 1: Co-precipitation Optimization Study OBJECTIVE: To optimize Cu and Zn co-precipitation with Al/Fe hydroxide TEST CONDITIONS: Intake sample Dissolved/total Cu 540/760 ppb 20% chelated Dissolved/total Zn ph /220 ppb Independent variables in the study ph Coagulant Coagulant concentration Detection method portable photometer YSI colorimetric reagents kits 15

16 Phase 1: Co-precipitation Optimization Study Test ph Al coag. #1 Al coag. #2 Fe coag. Diss. Cu, % Removal Diss. Zn, % Removal # ppm 81% 50% # ppm 52% 90% # ppm 63% 90% # ppm 70% 70% # ppm 48% 90% # ppm 74% 35% # ppm 74% 90% # ppm 81% 65% # ppm 100 ppm 67% 85% # ppm 100 ppm 85% 90% # ppm 100 ppm 74% 90% #1 vs. #10 Fewer steps (2 vs 4) As(VI) and Cr(VI) removal is known to be better at lower ph (but limited testing possible with a photometer) 16

17 Phase 1: Chemical Precipitation and Filtration 17

18 Phase 1: Field Results ppb Particulate Cu IN Average Removal, % Metal Total Dissolved As 83% 76% Cr 93% 87% Cu 85% 83% Zn 48% 18% IN Dissolved Cu OUT BCWQG As Cr Cu Zn OUT Discharge conc n of As, Cu, Zn, Cr BCWQG (LT) > BCWQGs 18

19 Phase 2: Fixed Bed Adsorption Method PROS Simplicity Low capital cost CONS Operating costs can be high Partial or complete system shutdown required to replace media Source: 19

20 Phase 2: Adsorption Optimization Studies OBJECTIVE: optimize Cu and Zn adsorption TEST CONDITIONS: Pre-treated intake sample (Phase I conditions) Dissolved/total Cu 160/160 ppb 20% chelated Dissolved/total Zn 200/200 ppb ph 6.5 Independent variables in the study Combination of Adsorbents Detection method portable photometer YSI colorimetric reagents kits RESULTS: a combination of adsorbents was found to reduce Cu and Zn to below detection limit (20 ppb) 20

21 Phase 2: Fixed Bed Adsorption Phase 2 21

22 Phases 1+2: Field Results Volume treated, L #1 #2 #3 #1 #2 #3 BCWQG (ST) Discharge BCWQG (ST) Discharge BCWQG (ST) Discharge 326, ,826 3,982,130 Hardness BCWQG (ST) Discharge BCWQG (ST) Discharge BCWQG (ST) Discharge Volume treated, L 326, ,826 3,982,130 Hardness As < As Cr (VI+III) < <0.1 < <1.0 Cr (VI+III) Cu < < < Cu Zn < < Zn 30 <5 30 < Below the Maximum Within 5% of the Maximum Exceeds Maximum by more than 5% 22

23 PPB Phase 1+2: Field Results for As 450 ARSENIC Total Metals Test Results & Removal Levels 105.0% % 99.7% 96.1% 98.9% 97.4% 99.4% 99.7% 98.7% 96.4% 100.0% 95.0% % % % % Nov.3/2016 Nov.14/2016 Jan. 24/2107 Feb. 2/2017 Feb. 15/2017 Intake (PPB) Phase 1 (PPB) Phase 2 (PPB) BCWQG Std Phase 2 (% remov) BCWQG (% remov) 75.0% 23

24 PPB Phase 1+2: Field Results for Cr CHROMIUM Total Metals Test Results & Removal Levels 101.0% % 100.0% 100.0% 100.0% 99.3% % 100.0% 99.0% % 98.0% % 95.9% 96.0% % Nov.3/2016 Nov.14/2016 Jan. 24/2107 Feb. 2/2017 Feb. 15/2017 Intake (PPB) Phase 1 (PPB) Phase 2 (PPB) BCWQG Std Phase 2 (% remov) BCWQG (% remov) 95.0% 94.0% 93.0% 92.0% 91.0% 24

25 PPB Phase 1+2: Field Results for Cu COPPER Total Metals Test Results & Removal Levels % % 99.4% 99.5% 99.5% 98.7% 98.9% 98.4% 100.0% % 95.0% % % 84.3% % % Nov.3/2016 Nov.14/2016 Jan. 24/2107 Feb. 2/2017 Feb. 15/2017 Intake (PPB) Phase 1 (PPB) Phase 2 (PPB) BCWQG Std Phase 2 (% remov) BCWQG (% remov) 75.0% 25

26 PPB Phase 1+2: Field Results for Zn ZINC Total Metals Test Results & Removal Levels % % 100.0% 100.0% % % 82.0% 77.5% 78.0% 80.0% 62.0% 60.0% % 52.5% % % Nov.3/2016 Nov.14/2016 Jan. 24/2107 Feb. 2/2017 Feb. 15/2017 Intake (PPB) Phase 1 (PPB) Phase 2 (PPB) BCWQG Std Phase 2 (% remov) BCWQG (% remov) 0.0% 26

27 Key Takeaways Chemical Co-Precipitation is a cost effective method for lowering metals conc ns Chemical Co-Precipitation alone is unlikely to be sufficient to meet BCWQGs for many heavy metals, including Cu, Zn, Cr, & As Chemical Co-Precipitation + Adsorption = a proven effective way to meet BCWQGs (for this project at ~ 20-30% cost of an RO system) Intake profile and contamination source play a very important role in treatment process design 27

28 Questions and Answers 28