Waste or Resource: Solid Energy’s Beneficial use of Waste Streams

Paul Weber1, Joe Wildy1, Fiona Crombie1, William Olds1, Phil

Rossiter1, Mark Pizey1, Nathan Thompson2, Paul Comeskey2, Dave Stone2, Andrew Simcock3, Andy Matheson1, Karen Adair4, Mark

Christison5, Hayden Mason6, Mark Milke7

1-Solid Energy New Zealand Ltd; 2-Stockton Alliance New Zealand Ltd; 3-Biodiesel New Zealand Ltd; 4-Bio-Protection Research Centre, Lincoln University;

5-Christchurch City Council; 6-Holcim New Zealand Ltd;

7-Department of Civil and Natural Resources Engineering, University of Canterbury

Correspondence to: paul.weber@solidenergy.co.nz

Presentation Overview

Solid Energy has investigated the beneficial reuse of waste streams for the last 10

years.

The work has focused on the mining operations, particularly the large environmental

liabilities associated with:

- Acid Mine Drainage (Prevention and Treatment)

- Rehabilitation of mine sites

Significant research has also been undertaken for the Solid Energy

Renewables Group

Overview of Solid Energy Operations

Biodiesel New Zealand Ltd

Natures Flame

Mining

Prevention of Acid Mine Drainage

Acid Mine Drainage

AMD is generated by pyrite oxidation

FeS2 + 7/2O2 + H2O Fe2+ + 2SO42- + 2H+ (H2SO4)

Pyrite + oxygen + water dissolved Fe + sulfate + acidity

Neutralisation can be achieved with limestone

CaCO3 + 2H+ Ca2+ + CO2 + H2O

Limestone + acidity dissolved calcium + CO2 + water

Fe2+ can create additional acidity by hydrolysis (Lewis acidity)

Fe2+ + 1/4O2 + H+ Fe3+ + 1/2H2O

Fe3+ + 3H2O Fe(OH)3(s) + 3H+ (occurs at ~ pH 3)

Any aluminium leached from minerals can also contributes to Lewis acidity

NaAlSi3O8 + 4H+ Na+ + Al3+ + 3SiO2(aq) + 2H2O (Al neutralisation)

Al3+ + 3H2O Al(OH)3 + 3H+ (occurs at pH 4-5) (Al acid formation)

0

1

2

3

4

5

6

7

8

0 1000 2000 3000 4000 5000 6000

Acidity (mg/L CaCO3)

pH

Egypt Pad 3 ARD

Al buffering

Fe buffering

AMD Minimisation – Engineered Covers

Typically acid forming rock dumps are

capped with 400 mm of weathered

granite to a permeability of 1 x 10-6 m/s

and covering with 300 mm of top soil.

High rainfall (6 m/year) allows for a

saturated cap to be maintained and

subsequently a reduction in oxygen

ingress and acid generation.

C Drive Dump – Granite cap with direct transfer soil

and vegetation – the best recycling possible

Stockton Collis Seep acid loads post capping

0

500

1000

1500

2000

2500

3000

3500

4000

4500

5000

17-Jun-07 21-Jul-08 25-Aug-09 29-Sep-10

Ac

idit

y t

o p

H 7

(m

g/L

Ca

CO

3)

Date

Acidity decrease with time due to reduced oxygen ingress following

capping

New AMD Prevention Technologies

using waste by-products

Cement Kiln Dust (CKD) – Holcim New Zealand Ltd

CKD Production - Holcim New Zealand Ltd

Engineered caps using CKD to control AMD

CKD is brought to site and is mixed with granite to

produced a capping material

Caps are 400 mm thick.

1:4 CKD:Granite produce 10-6 m/s permeability,

which reduces oxygen ingress

Coal ash (obtained from customers) can also be

used.

AMD prevention – alkaline oxygen excluding covers

Coal ash (CCP) and Cement Kiln Dust (CKD) are used at Stockton to create

alkaline oxygen excluding covers.

These caps produce alkalinity and neutralise AMD as well as excluding oxygen

Sample Paste pH ANC (kg H2SO4/t)

Various aglime products (<2mm) 8.4 - 10.8 747 - 966

CKD 11 - 13.9 479 - 788

Coal ash 5.96 - 11.96 24.5 – 354.2

BCM PAF sandstone control 3.3 <1

Oxy

gen

Conc

entr

atio

n (%

)

CCPCKDGraniteControl

20

15

10

5

0

2m deep oxygen probes

put into dumps.

M1 Overburden Dump – (5,000 tonnes of CKD)

CKD layer 300mm thick 230m long x 16m to 19m wide

Control Area No CKD layer

0

5

10

15

20

25

30

35

0 20 40 60 80 100

Weeks

Acid

Lo

ad

(g

CaC

O3) Control

CKD Treatment

Field trials have indicated that for 1:4 CKD:Granite

caps that:

The alkalinity release from the 1:4 cap is

~12 t CaCO3 per Ha per year.

Acid loads from the Mangatini catchment is

~30 t CaCO3 per Ha per year.

Use of CKD as a fill for underground workings Millerton historic underground mine

Issues include:

Underground fires

Safety issues for heavy

vehicles overtop

Reduces coal

contamination

>1 million m3 of voids

Stowage using CKD to fill voids – Holcim New Zealand Ltd

Overburden (-35) + Sand (-7)

H20

OPC

CKD

Stowage

• Up to 15 wt% CKD used as a binder to produce controlled low strength fill (CLSF)

• 30,000 – 40,000 tonnes per year will be beneficially reused once the project starts

Stowage – MG15 Trial

Fig 5a. CLSF as placed within the MG15 void Fig 5b. Exposed CLSF during mining (MG15)

CLSF (stowage) caps for AMD prevention

Condition Permeability (m s-1)

Capping 10-6.2

1 Stowing: 3 Capping 10-6.5

1 Stowing: 1 Capping 10-7.5

3 Stowing: 1 Capping 10-6.3

Stowing 10-6.3

This means the CKD is being

beneficially reused twice

1. Stowage

2. Capping

New AMD Treatment Technologies

using waste by-products

Treatment of AMD using a mussel shell reactor

Culvert Mussel shell

Direction of water flow

KEY:

100 – 200 mm water cover

Alkathene pipe Novaflow pipe Warratah

High-rainfall overflow

100 – 200 mm

water cover

160 tonnes of mussel shell

Mussel shell reactor

Effluent

Influent

Overflow

Mussel shell reactor: pH and acidity

1

3

5

7

9

14 113 345 503 657

pH

Time (days)

Influent Effluent Ford Creek

1

3

5

7

9

14 113 345 503 657

pH

Time (days)

Influent Effluent Ford Creek

0

300

600

900

1 35 282 429 587

Acid

ity (

mg

/L C

aC

O3)

Time (days)

Mussel shell reactor: metals

Mussel shell reactor – 2 years on

Carbonate Neutralisation Phase CaCO3 + 2H+ Ca2+ + CO2 + H2O

Sulfate Reduction Alkalinity Phase

SO42- + 2CH2O + B 2HCO3

- + H2S

Zone Depth Remnant ANC

mm kg CaCO 3 /t

Fe Sludge Layer 0 - 330 -5 na

Orange Fe Shell Layer 330 -350 459 carbonate

White Al Shell Layer 350 -500 499 carbonate

White Al Shell Layer 500 -600 825 Sulfate

Black Shell zone >600 846 Sulfate

Neutralisation

Phase

Whirlwind Mussel Shell Reactor

The technology has been rolled out as an operational tool for Stockton AMD treatment

Whirlwind Mussel Shell Reactor

Parameter Rough size

Average Plan Dimensions (m) 15.4 x 23.0

Average Plan Area (m2) 354

Average reactor depth (m) 2.4

Average Shell depth (m) 1.0

Ponding depth (m) 0.3-0.7

Average Freeboard (m) 1.1

Volume of shells (m3) 354

Mass of Shells (T) 325

Total ANC** (T CaCO3) 275

Whirlwind Seep Acid load (T CaCO3/yr) 5.2

Time to 10% exhaustion (years) 5.3

Whirlwind Mussel Shell Reactor

Treating flow rates up to 6 L/sec

Conventional AMD treatment using limestone

Data for the Ngakawau River compliance monitoring point

Conventional AMD treatment using limestone

2011 Ngakawau River Fish Survey Results

In 2005 AMD treatment had not commenced

This started in March 2007

Future Research: Mussel shells for AMD treatment

Sample ANC Efficiency

90% < 100 microns kg CaCO 3 /t %

Mussel shell powder 891 54

Ultrafine limestone 936 77

Mine site rehabilitation

using municipal biosolids

Biosolids for mine site rehabilitation - Rotowaro

Hamilton City Council aged biosolids (10 years)

Trial conducted from 2007 - 2009

• Municipal biosolids are a huge waste stream in New Zealand, often going to landfill

• Solid Energy has sites across the country that could use biosolids as a topsoil substitute

Stage 1: Placement of aged Hamilton Biosolids

Stage 2: Spreading Hamilton aged biosolids

Stage 3: Ripping in biosolids (to 300 mm depth)

Stage 4: Power harrow

Stage 5: Seeding

Plot established December 2007

Plots established using 0, 50, 100, 200, 400 dry tonnes/ha application rates

Rotowaro Biosolids June 2008 (month 6)

Control 50 dry

tonnes/ha 400 dry

tonnes/ha

200 dry

tonnes/ha

100 dry

tonnes/ha

Great vegetation growth and reduced erosion

All soil contaminants below ceiling limits set by Waikato Regional Council

Elevated rates of nitrogen loss for high application rates

Incorporation of biosolids was a machinery intensive process

Key conclusion was that surface application at low rates may be more suitable

Surface application trials 2009 to 2012

Two surface application trials were undertaken between 2009 to 2012 to 40ha at

Waipuna

- 2009/2010 Field trial to evaluate low-dose repeat surface applications of biosolids (200 kg

N/ha.yr) 19 wet tonnes per hectare (4 dry tonnes / ha)

- 2010/2011 Field trial to evaluate low-dose repeat surface applications of biosolids (400 kg

N/ha.yr) 38 wet tonnes per hectare (8 dry tonnes / ha)

The trial objectives were:

Determine operational deployment process and economics

Vegetation response

Soil contaminant levels (organics/metals)

Rates of nitrogen loss

Operational deployment

Operational deployment

Operational deployment (spread)

Vegetation response (control site)

Vegetation response (application area)

Inorganic soil contaminants to February 2012

Consent Limit

Soil Concentration (after 57 wet tonnes)

Results are comparable to baseline values

Organic soil contaminants to February 2012

Consent Limit

Soil Concentration (after 57 wet tonnes)

Results are comparable to baseline values

Nitrogen loss to surface water – used to calculate nitrogen loss per year

Surface application trials 2009 to 2011 Summary

The 2009 -2011 field trials found that nitrogen loss beyond the CML

boundary did not exceed 8 kg N/ha/yr

This is significantly lower than surrounding agricultural discharges which

are likely to be at least 30 kg N/ha/yr (pers.comm. WRC)

All metals and organic contaminants are well below the agreed ceiling

limits set with Waikato District Council

Solid Energy has applied for consents to go operational at Rotowaro

Stockton Biosolids Project - Christchurch City Council

The $30M Bromley biosolids thermal drying facility

Thermally dried biosolids

have essentially zero

pathogens

Establishing field trial plots - January 2009

Biosolids are mixed directly with waste overburden from the site (no soil)

Establishing field trial plots - January 2009

Blending in 270 dt/ha of biosolids pellets into mine spoil

Establishing field trial plots – Planting March 2009

Field trial plots, Stockton Vegetation cover by month 8, October 2009

Field trial plots, Stockton

Field trial plots, Stockton

Operational use of biosolids has started at Stockton (6,000 tpa)

Solid Energy Renewables Group

Nature’s Flame Wood Pellet Production - 2011

Taupo Wood Pellet Plant

Key Production Statistics

– 30Ktpa in 2012, moving to 360ktpa (site potential 760ktpa);

– Automated: 2-3 staff

– Close to Ports & feedstock

Biodiesel New Zealand Ltd

BDNZ capacity up to 4 million L pa of biodiesel

FY11 production was 2 ML

10% of production is biodiesel glycerol

A beneficial use for the waste biodiesel glycerol was required

100kg Oil + 10kg Methanol (+ catalyst) = 100 kg Biodiesel + 10kg glycerol

Anaerobic digestion of glycerol to produce energy

Figure 6a. Laboratory biogas production for raw sewerage co-digested with glycerol

Figure 6b. Bromley biogas production and significant increases in gas following the addition of glycerol.

Collaboration with the Department of Natural and

Civil Engineering, Canterbury University

At 3% feed there was a 200% increase in methane

0.2 – 0.35 m3 CH4 / kg COD

Biodiesel glycerol has a COD of 2.1 kg/L

Field trials at the Christchurch City Council Bromley Plant

Figure 6a. Laboratory biogas production for raw sewerage co-digested with glycerol

Figure 6b. Bromley biogas production and significant increases in gas following the addition of glycerol.

Biosolids as a fertiliser for Biofuel Crops

Figure 7 – Mean seed yield per C. sativa (left) and B. napus (right) plant when grown in control soil, with urea fertiliser and two levels of biosolids (low: 200 kg ha-1 N equivalent and high: 400 kg ha-1 N equivalent applied prior to sowing

Research in collaboration with Bio-Protection Research Centre, Lincoln University

Potential to use bisolids to grow biofuel crops on marginal land

Full Cycle

Solid Energy NZ Ltd

(Coal)

Cooking oil

Waste cooking oil Biodiesel GlycerolAnaerobic

Digestion

Methane

(Energy)

Biodiesel New Zealand Ltd Christchurch City Council

Transport

fuel District Heating

or Energy

Mine Site

Rehabilitation

(Stockton)

Drying of

Biosolids

Biofuel crops

Solid Energy and Chrichurch City Council beneficial reuse synergies

Conclusions

Waste products beneficially reused by Solid Energy (since 2006). All values are total tonnes to date

except where indicated by tpa (tonnes per annum).

Over 200,000 tonnes of waste products have been beneficially reused by Solid Energy

Waste Product (diverted for beneficial reuse to date) Tonnes (approx.)

Biosolids 4,600

Coal Ash 9,100

Cement Kiln Dust 90,000

Mussel Shells 800

Waste Cooking Oil 6,000 tpa

Glycerol 400 tpa

Wood offcuts (sawdust, shavings etc) 150,000

Compost (derived from composting organic waste from freezing works) 3,000 tpa

Acknowledgements

Stockton Alliance Ltd

Biodiesel New Zealand Ltd

Natures Flame

Holcim New Zealand Ltd

Christchurch City Council

Bio-Protection Research Centre - Lincoln University

Natural and Civil Engineering School - Canterbury University

Further information:

Dr Paul Weber

Technical Services Group, Solid Energy

paul.weber@solidenergy.co.nz