Laboratory trials in support of research on use of mine water in wastewater treatment

Background

• Coal Authority treats c.122billion

litres of water a year

• Treating former coal mine waters

generates many thousands of

tonnes of hydrous ferric oxide

(HFO) every year

• HFO has multiple adsorption

sites that can remove phosphate

as well as other substances

Project Background

• Lamesley mine water treatment scheme

has removed P from tertiary waste water

effluent for over 10 years

• This study was developed to identify if

mine water could both support P removal

and help coagulation in primary settlement.

• This project is in collaboration with

Yorkshire Water, concentrating on mine

water sites close Yorkshire Water

wastewater treatment works.

Aim & ObjectivesThe aim of this project is to investigate the characteristics of minewater and ochre derived from

minewater treatment and evaluate if either are of benefit in the removal of total phosphorus in

wastewater treatment process. To achieve this aim the following objectives have been set;

• Assess the potential of minewater to wholly, or partially, replace ferric salts for the treatment of

wastewaters

• Identify the appropriate ratio (or range of ratios) of minewater to wastewater required for efficient and

cost-effective treatment.

• Characterise the chemistry of the resultant treated discharge water

• Characterise the chemistry and physical properties of the resultant sludge

• Assess the environmental implications of using minewater in wastewater treatment with respect to

treated effluent discharge quality and sludge management

Methodology - Characterisation

• Characterisation of a selection of minewater samples • Woolley

• Bullhouse

• Strafford

• Sheephouse

• Bullhouse ochre

• Characterisation of a crude sewage• High incoming phosphorus concentration - Sherburn in Elmet WwTW

• Low incoming phosphorus concentration – Stocksbridge WwTW

Methodology – Jar Testing• 6 No. 1 litre jars to achieve the required iron:phosphate ratio (2-6 molar ratio)

• A volume of minewater or ochre added with either Stocksbridge or Sherburn in Elmet crude wastewater to 1 litre jar

to achieve the correct molar ratio

• Flash mix 100rpm– 2 minutes

• Flocculate 30rpm – 15minutes

• Quiescent Settlement – 30 minutes

• 52 scenarios, detailed analysis was carried out to determine characteristics of the supernatant and the settled solids

• Control

• Ochre

• 2 No. minewaters that demonstrated the best phosphorus removal for Sherburn in Elmet and Stocksbridge.

Minewater/Ochre Iron:Phosphate

Ratio

Stocksbridge WwTW (low

phosphorus site)

Control 0

Ochre 2,3,4,5,6

Woolley 2,3,4,5,6

Strafford 2,3,4,5,6

Bullhouse 2,3,4,5,6

Sheephouse 2,3,4,5,6

Sherburn in Elmet WwTW (low

phosphorus site)

Control 0

Ochre 2,3,4,5,6

Woolley 2,3,4,5,6

Strafford 2,3,4,5,6

Bullhouse 2,3,4,5,6

Sheephouse 2,3,4,5,6

Methodology – Treatability Trial• 2 No. bench scale activated sludge reactors

• 10 litres in capacity

• Diffused aerators to mimic fine bubble diffused aeration in an activated sludge plant

• Both reactors operated for 7 days continuously

Feed Type food:mass ratio HRT

Rig 1 Supernatant from the

optimum scenario (section

2.2)

0.08 8

Rig 2 Wastewater only 0.1 19

Analysis Frequency

MLSS MLSS mg/l

MLVSS mg/l

SSVI ml/g

D.O. mg/L

Temp oC

3x week

3x week

Once

Daily

Daily

Final Effluent BOD mg/L

COD mg/L

pH

Ortho P mg/l

TSS mg/L

2x week

3x week

3x week

2x week

3x week

Characterisation Results

Total

Iron

Soluble

Iron

Total

Phosphorus

Ortho-

Phosphate

TSS COD Ammonia

mg/l mg/l mg/l mg/l mg/l mg/l mg/l

Stocksbridge

WwTW

1.62 0.671 6.95 3.7 190 530 20.6

Sherburn in Elmet

WwTW

1.04 0.316 7.3 4.5 233 626 32.1

Wastewater

• The analysis showed phosphorus concentrations for both sites were actually very similar, this was deemed not to be a critical factor in the project.

Minewater and ochre

• Minewater composition is variable and these results are representative of the conditions

at the time the sample was taken. Future samples may provide slightly different resultsTotal Iron Soluble Iron Total Phosphorus Ortho-Phosphate

mg/l mg/l mg/l mg/l

Sheephouse 52.7 56.8 0.46 0.14

Bullhouse 28.3 26.76 0.23 0.09

Strafford 7.26 1.068 0.11 0.03

Woolley 5.5 0.01 0.13 0.12

Bullhouse Ochre 59840 155

Jar Test Results - Stocksbridge

-40%

-20%

0%

20%

40%

60%

80%

2 3 4 5 6

Ort

ho p

hosphate

% r

em

oval

Molar Ratio (Iron:Phosphate)

Stocksbridge Minewater Ortho Phosphate removal %

Sheephouse Bullhouse MW Strafford

Woolley Bullhouse Ochre

• Minewater that achieved the best ortho phosphate removal was Sheephouse at 35-69%

• Bullhouse Ochre also had the second highest ortho phosphate removal at 8-39%

• The optimum iron:phosphate ratio for both of these conditions was 6.

Jar Test Results – Sherburn in Elmet

• Minewater that achieved the best ortho phosphate removal was Bullhouse ochre at 15-39%

• Bullhouse minewater also had the second highest ortho phosphate removal at 0-32%

• The optimum iron:phosphate ratio for both of these conditions was 6

• Reason for a lower removal efficiency when compared to Stocksbridge is unknown. Wastewater composition maybe a factor

-80%

-60%

-40%

-20%

0%

20%

40%

60%

2 3 4 5 6

Ort

ho p

hosphate

% r

em

oval

Molar Ratio (Iron:Phosphate)

Sherburn in Elmet Minewater Ortho Phosphate removal %

Sheephouse Bullhouse MW Strafford Woolley Bullhouse Ochre

Results – Minewater Dilution

• For all but Sheephouse the minewater added was over 50% of the total jar volume . This had a dilution effect on the jars with regards to ortho phosphate.

• Highlights a hydraulic concern at full scale, most wastewater treatment works have minimum hydraulic retention time criteria • Primary settlement = 2hours• Activated sludge systems = 10 hours respectively.

Volume added to 6 molar ratio jar

Stocksbridge

Wastewater (ml)Minewater (ml)

Sherburn in Elmet

Wastewater

(ml)

Minewater (ml)

Sheephouse512 388 468 432

Bullhouse373 527 331 569

Strafford138 762 117 783

Woolley109 791 91 809

Jar Test Detailed Analysis - Stocksbridge• Sheephouse minewater and Bullhouse ochre at molar ratio of 6

with Stocksbridge

• Supernatant and settled solids for detailed analysis

• Ortho phosphate 73% removal with Sheephouse minewater at a molar ratio of 6

• Ortho phosphate 79% removal with Bullhouse ochre at a molar ratio of 6.

• Settlement alone only provided 11% ortho phosphate removal.

• Sheephouse and Bullhouse ochre blend total phosphorus was 2.34mg/l and 2.99mg/l respectively

• Sheephouse and Bullhouse ochre blend total iron was 5.95mg/l and 4.41mg/l respectively

• Sheephouse Minewater blend supernatant

• Nickel was above the EA recommended surface water levels, 26ug/l exceeding the 20ug/l limit

• Sulphate concentration was 313mg/l. Very high compared to the typical wastewater concentration of 50mg/l

Surface Water Limit

(ug/l)

Arsenic (inorganic) 10

Barium 700

Boron 1000

Cadmium 100

Copper 1-28

Lead 7.2

Mercury 10

Nickel 20

Zinc 8-128

Jar Test Detailed Analysis – Sherburn in Elmet• Bullhouse minewater and Bullhouse ochre at molar ratio of 6 with

Sherburn in Elmet

• Supernatant and settled solids for detailed analysis

• Ortho phosphate 25% removal with Bullhouse minewater at a molar ratio of 6

• Ortho phosphate 70% removal with Bullhouse ochre at a molar ratio of 6.

• Settlement alone only provided 12% ortho phosphate removal.

• Bullhouse minewater and Bullhouse ochre blend total phosphorus 2.06mg/l and 3.77mg/l respectively

• Bullhouse minewater and Bullhouse ochre blend total iron was 19.7mg/l and 2.06mg/l respectively

• Bullhouse Minewater blend supernatant

• Nickel and Arsenic was 51ug/l and 19mg/l respectively exceeding the 20ug/l limit for Nickel and the 10mg/l limit for Arsenic

• Sulphate concentration was 446mg/l. Very high compared to the typical wastewater concentration of 50mg/l

Surface Water Limit

(ug/l)

Arsenic (inorganic) 10

Barium 700

Boron 1000

Cadmium 100

Copper 1-28

Lead 7.2

Mercury 10

Nickel 20

Zinc 8-128

Treatability Results• The treatability trial involved 2 No. bench scale activated sludge reactors

• Rig 1 Supernatant from Stockbridge/Sheephouse blend (molar ratio 6)

• Rig 2 Stocksbridge wastewater only

• The BOD removal for both rigs was over 90% and the COD removal remained above 79%

• Detailed analysis of supernatant rigs 1 and 2• Rig 1 = significant ortho phosphate removal, 68%

• Rig 2 = 0% ortho phosphate removal

• The total phosphorus and total iron concentrations in the final effluent from Rig 1 were also below the typical consent for values of 1mg/l total phosphorus and 4-6mg/l total iron at 0.78mg/l and 1.89mg/l respectively

• Sulphates in the final effluent • Rig 1 = 330mg/l

• Rig 2 =94mg/l

• Rig 1 settled solids, as an indication zinc and copper concentrations exceed the maximum permissible concentrations for sludge to land at 200 mg/kg and 80mg/kg respectively

Conclusions• Main conclusion is that minewater does show some potential for the removal

of orthophosphates from wastewater. However, it is unlikely to be feasible at full scale due to the hydraulic issues.

• Wastewater treatment works with sufficient hydraulic capacity further investigation into the fate of the metals from the mine water and the impact of sulphate on odour conditions at the wastewater treatment works.

• Ochre also showed some potential for phosphorus removal. • Ochre would not present the same hydraulic issues.• Sulphate is also lower in the ochre as sulphate will be mainly soluble

• It is recommended that the ochre be investigated to determine any biological impacts and the fate of metals in the ochre in the final effluent and sludge

• Cost associated with ochre being provided in wastewater treatment needs to be determined and compared to the OPEX costs of dosing a ferric chemical to achieve the equivalent ortho phosphate removal of 40-80%

Next Steps

• Further investigation for mine water generated HFO use in cake or granular form for P removal in primary treatment

• Investigation of lime rich mine water cake for improving P removal and alkalinity balance to offset ferric and hydroxide

Questions?

Susan Davies – Process Manager

susandavies@aquaenviro.co.uk

Peter Thorn – Principal Innovation Technical Manager

peterthorn@coal.gov.uk