Basic Oxygen Furnace steel slag and apatite for sustainable - PowerPoint PPT Presentation

Basic Oxygen Furnace steel slag and apatite for sustainable phosphorus removal at small wastewater treatment plants SWWS2016 Naiara Fonseca PhD student 15 th September 2016

Background Why remove phosphorus and to what extent? • The largest source of phosphorus (P) in rivers in the UK is sewage effluent • Current consents based on the Urban Wastewater Treatment Directive WWTP size (population equivalent) Total Phosphorus consent (mg/L) < 10,000 none 10,000 – 100,000 2 > 100,000 1 • Water Framework Directive – Good ecological status • New TP consents 1-2 mg/L, and as low as 0.5 mg/L regardless of WWTP size 2

Solutions to remove P at small WWTP Conventional solution: chemical dosing + tertiary filtration Coagulant Coagulant Sand filter Screens Trickling Humus Primary Filters tanks Settlement Tanks 3

Solutions to remove P at small WWTP Conventional solution: chemical dosing + tertiary filtration 4

Solutions to remove P at small WWTP Sustainable solution: Constructed wetlands with reactive media Constructed Screens Trickling Humus tanks Primary wetlands with P Filters Settlement reactive media Tanks 5

Solutions to remove P at small WWTP Sustainable solution: reactive media within constructed wetlands BASIC OXYGEN APATITE FURNACE STEEL SLAG 6

Solutions to remove P at small WWTP Sustainable solution: reactive media within constructed wetlands BASIC OXYGEN APATITE FURNACE STEEL SLAG Material Origin Type of material Price BOF steel slag Tarmac (Wales) Waste £ Apatite TIMAB (France) Manufactured £££ 7

Full-scale constructed wetland trial Configuration < 10% of Q T TP = 3 - 4 mg/L Bed Material Type vHRT (h) Days in operation 1 SS 10 ‐ 20mm 24 379 2 SS 4 ‐ 10mm 24 374 Horizontal sub ‐ surface flow 3 SS 2 ‐ 6mm 24 291 4 Apatite 2 ‐ 8mm 12 404 8

Lab-scale column experiments Configuration Column Material vHRT (h) Flow Water type Days in operation 1 SS 4 ‐ 10mm 6, 24, 48 Downwards, Synthetic, 45 submerged NH 4 H 2 PO 4 2 Apatite 2 ‐ 8mm 60 3 Apatite2 2 ‐ 8mm 6 9

Full-scale constructed wetland trial Results • All slag fractions <0.5 mg/L for most of the time. Apatite consistently <0.5 mg/L • Apatite higher P removal capacity than slag • 10 Conditioning period

Full-scale constructed wetland trial Results • High effluent pH linked to Ca(OH) 2 dissolution • Effluent pH decrease with time for both materials, but higher for apatite and <9 11

Full-scale constructed wetland trial Results – Phosphorus removal • Removal efficiency: apatite > small slag > medium slag > large slag 12

Lab-scale column experiments Results – Effect of HRT on steel slag performance • Higher P removal for higher HRT • Higher effluent pH for higher HRT 13

Lab-scale column experiments Results – Effect of HRT on apatite performance • High P removal regardless of HRT • Higher effluent pH for higher HRT, but lower than slag 14

Lab-scale column experiments Results – comparison of two different apatite materials • So far, same P removal for both apatite materials • Apatite2 lower effluent pH linked to the binder employed (Fe based instead of Ca based) 15

Conclusions • Constructed wetlands with reactive media can be a sustainable and appropriate solution for P removal at small WWTPs. • BOF steel slag could be employed for consents > 1.5 mg TP/L. • Apatite shows higher P removal capacity than BOF steel slag. • HRT key operational parameter for slag, but less for apatite. • New apatite generation produces lower effluent pH while maintaining same high level of P removal. 16

Basic Oxygen Furnace steel slag and apatite for sustainable phosphorus removal at small wastewater treatment plants THANK YOU FOR YOUR ATTENTION Naiara Fonseca Naiara.FonsecaGalarraga@thameswater.co.uk N.Fonseca@cranfield.ac.uk 17