improving sludge treatment whole life cost savings by way ...€¦ · we have considered the...

HUBER Technology UK – www.huber.co.uk

Improving sludge treatment whole

life cost savings by way of

dewatering on satellite sites

http://www.huber.co.uk/


Slide 2

Present situation

• In order to optimise methane production and sludge quality for disposal, the

UK has seen a trend towards large, regional sludge reception facilities with

some form of Advanced Anaerobic Digestion (AAD) (e.g. with Enzymic or

Thermal Hydrolysis pre-treatment).

• These facilities involve significant CAPEX and it is more economically viable

to have only a few of these huge capacity sites and bring in sludge from

outlying satellite works.

• The transportation costs incurred by such sludge movement are significant

and obviously get higher if the sludge is thinner and if the satellite sites are a

long way from the AAD plant.

• Some water companies are already using satellite site sludge dewatering to

reduce volumes for transport followed by “re-wetting” at the AAD site to give

the required feed thickness.



Slide 3

Present situation

A cake reception area (as shown in these examples) and re-wetting facility are

an additional CAPEX required at the AAD plant.

United Utilities - Davyhulme WwTW

Northumbrian Water – Bran Sands WwTW Dwr Cymru - Afan WwTW



Slide 4

Drivers for dewatering at satellite sites

If practical and if the payback period is acceptable, upgrading satellite sites to

include some form of volumetric reduction of the sludge being produced:

• Can significantly reduce the whole life cost of the plant as a result of reduced

transportation costs,

• Can reduce the indirect carbon footprint of the AAD plant as a result of fewer

lorry movements (against which the increased power consumption etc. at the

satellite sites is insignificant),

• Can help the water company achieve it’s AMP6 goal to improve efficiency

(by reduced OPEX).

Dewatering is likely to only be favored over thickening or optimizing the existing

set-up if the overall whole life cost saving is significant and if the payback period

is sufficiently short (3-7yrs).



Slide 5

UKWIR report

This presentation makes use of data and findings in UKWIR report no.

13/SL/11/6 –

“Sustainable Sludge Thickening and Treatment at Small WwTWs”

Available from:

http://ukwir.forefront-library.com/reports/13-SL-11-6/96374












Slide 6

UKWIR report

Excellent info but suppliers’ sizing and process data (i.e. cake dryness)

limited by not wanting to promise too much based on general scenarios.

The disposal costs used in the report are higher than those used by at least

one water company (hereafter referred to as “Alternative Costs” when used)

so this presentation will use both for comparison.

The report also discusses using mobile kit for volumetric production that

would be moved from site to site as required but, in practice, we have found

that this concept can be limited by:

• Changes to management personnel

• Operators on subsequent sites not having the required training and

• Subsequent sites needing different polymers which may mean that the

poly kit should really be cleared out first.



Slide 7

Pertinent info from UKWIR report 13/SL/11/6

Of the 7 water companies who provided info:

• The no. of sites with a pop. smaller than 2,000 ranged from 191 to 1727 (58 –

89 % of all the sites in each area),

• The no. of sites with a pop. between 2,000 and 10,000 ranged from 32 to 197

(5 – 24 % of all the sites in each area) and

• The no. of sites with a pop. between 10,000 and 25,000 ranged from 12 to 61

(2 – 5 % of all the sites in each area).

• On all 2k, 10k and 25k sites, 60-65% sites co-settle Primary and Humus

sludges.

• 15%, 20% and 25% of 2k, 10k and 25k sites, respectively, produce separate

Primary and Activated sludges.

Sludge production rates varied from 60 to 85 g/head/d but the majority were in

the 60 – 65 g/h/d range.



Slide 8

Pertinent info from UKWIR report cont.

• 50-75% of 2k to 10k sites have at least consolidation tanks (i.e. with

decanting valves)

• 75-100% of 10k to 25k sites have at least consolidation tanks.

• <25% of 2k to 10k sites have more reliable sludge thickening than

consolidation tanks

• Only 25-50% of 10k to 25k sites have more reliable sludge thickening

than consolidation tanks.

<25% of 2k, 10k and 25k sites:

• Are manned permanently,

• Have sludge screening,

• Have dewatering facilities already



Slide 9

Potential limitations to upgrading

Infrequent attendance and the lack of sludge screening on many small to

medium sites mean that all process steps in any upgrade solution:

• Should be simple and not require regular attendance or operator

interaction.

• Should be robust against rags and process fluctuations without the need

for setting adjustments and not prone to spills (that won’t be immediately

cleared-up) should anything go wrong.

• Should be slow moving and physically robust so as to minimise the

likelihood of mechanical wear and failure (due to the potential delay in

maintenance staff being able to attend site to rectify the problem).



Slide 10


The physical size of small to medium sites and their potential remoteness

mean that all process steps in any upgrade solution:

• Should have a small footprint.

• Should require little power.

• Should require little or no water and should be able to make use of final

effluent rather than potable where water is needed.

• Should not add to the load at the inlet works by-way of a poor Solids Capture

Rate.

• Should have a relatively short-term payback period that justifies the site

upgrade when small sludge volumes are involved.

There may also be insufficient room for lorries to manoeuvre on the particularly

small sites.



Slide 11


Assuming that there is sufficient space, water and power for site

upgrading in the form a thickener and/or dewaterer:

• Some means of homogenizing the feed sludge and therefore preventing

stratification and “rat-holing” should be provided (so as to promote

efficient operation).

• In the case of upgrading to dewatering, some means of thickening the

raw sludge(s) should be provided so as to maximise cake dryness and

minimise the overall footprint.

• Cake storage facilities should have sufficient volume to cater for several

days without a lorry driver being able to get to site to remove the cake.



Slide 12

Huber solutions used for cost comparisons

These machines “tick the relevant boxes” on the previous slides.

Thickening for small to medium sites:

RoS2S Disc Thickener – Fully enclosed, very simple & slow moving, lowest

power demand, rigid screening medium with ragging-resistant ploughs, low

water demand and lowest poly consumption.

Dewatering for small to medium sites:

RoS3Q and RoS3 Screw Presses/Drum Dewaterers - Fully enclosed, very

simple & slow moving, low power demand, rigid screening medium, ragging

not an issue, low water and poly consumption.

RoS2S Disc

Thickener

RoS3Q Screw Press Dewaterer

(for smaller throughputs)

RoS3 Screw Press

Dewaterer



Slide 13

Cake handling solution used for comparisons

• Skips may not be the best solution (no means of evenly distributing cake if no

operator present, open to atmosphere, require specialist wagon for swapping

over and have limited volume).

• Agrivert’s cake silo and conveyor package is ideal if there is sufficient space

(for lorry movements as well). The smallest unit is for 60m3 BUT if the demand

is there they will look at including smaller units in their range (assumed costs

for 20 and 40 m3 units have been used in the comparisons).

Cake silo Lorry loading



Slide 14

Whole life cost comparison scenarios

We have considered the following scenarios for Co-settled sites:

• Leave the site as is (i.e. typically with a relatively inefficient consolidation

and inefficient tankering off-site) – this is the scenario that all other

Solutions will be compared against.

• Solution 1: Optimise the existing set-up (e.g. improve/install automatic

decanting and/or instal %DS monitoring on the PST de-sludging and

convert the consolidation tank to a mixing tank if possible.

• Solution 2: Solution 1 followed by Disc thickening and a mixed storage tank

(for ease of tanker pumping).

• Solution 3: Solution 1 followed by Screw Press dewatering and a cake

storage solution.



Slide 15

Whole life cost comparison scenarios

We have considered the following scenarios for Activated Sludge sites:

• Leave the site as is.

• Solution 1: Improve PST de-sludging & Disc thicken the SAS, pump both

thick sludges into a sufficiently large mixing buffer tank ready for removal

by tanker (it may be possible to use an existing consolidation tank if it is

large enough but we’ve assumed a new tank would be required as a worse

case).

• Solution 2: Improve PST de-sludging & Disc thicken the SAS, pump both

thick sludges into a sufficiently large mixing buffer tank (again, it may be

possible to use an existing consolidation tank but we’ve catered for a new

tank), dewater the mixed sludge by Screw Press followed by a cake

storage solution.



Slide 16

Scope of comparisons

Our whole life cost comparisons:

• Consider sites with Population Equivalents of 2,000, 10,000 and 25,000 so as

to tie-in with the UKWIR report.

• Consider Co-settling on 2,000 and 10,000 sites but consider both Co-settling

and an Activated Sludge process on 25,000 sites (as a result of the stats

provided in the UKWIR report).

• Have evaluated transport distances of 30, 40 and 50km.

• Have used both the disposal costs used in the UKWIR report and the

Alternative Costs provided by a water company.

• Have looked at the payback periods required to achieve savings when a cake

reception and re-wetting facility already exists and also how many sites would

need to be upgraded to achieve various payback periods if a new cake

reception and re-wetting facility had to be built (whilst considering the report

stats regarding how many sites are actually out there).



Slide 17

Assumptions and costs used

We have assumed:

• That as the site size increases, the effectiveness of the existing set-up (i.e.

consolidation tank) improves a little due to increased staff attendance (more

regular manual decanting/removal of blockages).

• That Huber kit have their 2 and 5 year spares replaced at those intervals.

• That overall sludge production is 65 gDS/PE/d in-line with the UKWIR report.

• That primary sludge production is 40 gDS/PE/d.

• That primary/co-settled sludge is typically at 1.25% DS and SAS is at 0.7%.

• That concrete hard standing and a building costs ~£100/m2

• That sludge storage tanks cost ~£100/m3

• That installing a mixer costs ~ £15k

• That a payback period of between 3 and 7 years would be required.

All CAPEX relating to proprietary equipment is obviously commercially sensitive

but has been based on actual order and quote prices for individual components

where possible.



Slide 18

Existing cake reception & re-wetting facility

Existing set-upOptimised

de-sludgingDisc thickening

Screw press

dewatering

Payback period

> 7 years

Payback period

≤ 7 years

Overall whole life

saving > 50%

Colour key for the following four tables:



Slide 19

Summary for 2,000 P.E. – Co-settled


Existing set-up: Partial thickening in

Consolidation tank

Solution 1: Transport after efficient

de-sludging (if viable)

Solution 2: All Disc thickened (to

5.5% DS max. for tankering) after

efficient de-sludging & mixer in

consolidation tank

Solution 3: Screw dewatering after


consolidation tank

Produced DS % 2 4.5 5.5 25

Weekly production rate m3/wk 46 20 17 4

OPEX £/yr £11,863 £5,272 £6,385 £3,309

Payback period Yrs NA 4 25 20

Expediture over 25 yrs £ £296,563 £131,806 £294,164 £245,315

Saving over 25 yrs % NA 56% 1% 17%

OPEX £/yr £14,804 £6,580 £5,369 £3,893




OPEX £/yr £13,642 £6,063 £7,032 £3,451




OPEX £/yr £17,651 £7,845 £6,401 £4,196




OPEX £/yr £15,421 £6,854 £7,679 £3,593




OPEX £/yr £20,498 £9,110 £7,434 £4,498




UKWIR report costs

Alternative costs

UKWIR report costs

Alternative costs

30km transport distance



UKWIR report costs

Alternative costs



Slide 20




Consolidation tank






consolidation tank



consolidation tank

Produced DS % 2.5 4.5 5.5 25


OPEX £/yr £47,450 £26,361 £25,551 £9,825


Expediture over 25 yrs £ £1,186,250 £659,028 £800,902 £460,470


OPEX £/yr £59,218 £32,899 £26,843 £12,746




OPEX £/yr £54,568 £30,315 £28,786 £10,537




OPEX £/yr £70,606 £39,225 £32,006 £14,260


Expediture over 25 yrs £ £1,765,140 £980,633 £1,057,608 £571,347


OPEX £/yr £61,685 £34,269 £32,022 £11,248




OPEX £/yr £81,994 £45,552 £37,168 £15,774


Expediture over 25 yrs £ £2,049,840 £1,138,800 £1,186,663 £609,203



UKWIR report costs

Alternative costs


UKWIR report costs

Alternative costs


UKWIR report costs

Alternative costs



Slide 21




Consolidation tank






consolidation tank

Solution 3: Dewatering by Screw

Press after efficient de-sludging and

mixer installed in existing

consolidation tank

Produced DS % 3 4.5 5.5 25


OPEX £/yr £98,854 £65,903 £61,507 £21,091




OPEX £/yr £123,370 £82,247 £74,695 £28,393




OPEX £/yr £113,682 £75,788 £69,596 £22,870




OPEX £/yr £147,095 £98,063 £87,601 £32,179


Expediture over 25 yrs £ £3,677,375 £2,451,583 £2,365,327 £1,074,318


OPEX £/yr £128,510 £85,674 £77,684 £24,650

Payback period Yrs NA 1 3-4 3



OPEX £/yr £170,820 £113,880 £100,506 £35,964


Expediture over 25 yrs £ £4,270,500 £2,847,000 £2,687,963 £1,168,958


Alternative costs

UKWIR report costs


Alternative costs

UKWIR report costs


Alternative costs

UKWIR report costs




Slide 22

Summary for 25,000 P.E. – Mixed



Consolidation tank


Primary de-sludging and Disc

thickening of SAS


efficient Primary de-sludging & Disc

thickening of SAS

Produced DS % 3 4.98 27

Weekly production rate m3/wk 379 228 42

OPEX £/yr £98,854 £63,927 £22,601

Payback period Yrs NA 5 6

Expediture over 25 yrs £ £2,471,354 £1,756,225 £1,061,946

Saving over 25 yrs % NA 29% 57%

OPEX £/yr £123,370 £78,699 £29,362




OPEX £/yr £113,682 £72,862 £24,248




OPEX £/yr £147,095 £92,995 £32,867




OPEX £/yr £128,510 £81,797 £25,896




OPEX £/yr £170,820 £107,291 £36,372




UKWIR report costs

Alternative costs


UKWIR report costs

Alternative costs


UKWIR report costs

Alternative costs




Slide 23

No. of 10k P.E. Co-settled satellite sites requiring installation of

dewaterers in order to provide an acceptable payback period.*

•Assuming the cake reception and re-wetting facility are built on a 30,000 tDS/annum sludge facility.

** Not feasible as in significantly more than 50 sites would require upgrading to having dewaterers.

UKWIR

disposal

costs

30km

Alt.

disposal

costs

30km

UKWIR

disposal

costs

40km

Alt.

disposal

costs

40km

UKWIR

disposal

costs

50km

Alt.

disposal

costs

50km

No. of plants to

give 7 yrs

payback

36 16 19 10 13 7

No. of plants to

give 6 yrs

payback

Not

feasible**27 35 14 20 10

No. of plants to

give 5 yrs

payback

Not

feasible**

Not

feasible**

Not

feasible**26 46 15

No. of plants to

give 4 yrs

payback

Not

feasible**

Not

feasible**

Not

feasible**

Not

feasible**

Not

feasible**34

No. of plants to

give 3 yrs

payback

Not

feasible **

Not

feasible **

Not

feasible **

Not

feasible **

Not

feasible **

Not

feasible **

No existing cake reception & re-wetting facility



Slide 24

No. of 25k P.E. Co-settled satellite sites requiring installation of

dewaterers in order to provide an acceptable payback period.*



UKWIR

disposal

costs

30km

Alt.

disposal

costs

30km

UKWIR

disposal

costs

40km

Alt.

disposal

costs

40km

UKWIR

disposal

costs

50km

Alt.

disposal

costs

50km

No. of plants to

give 7 yrs

payback

7 5 5 4 4 3

No. of plants to

give 6 yrs

payback

9 6 7 5 5 4

No. of plants to

give 5 yrs

payback

15 9 10 6 7 5

No. of plants to

give 4 yrs

payback

42 16 19 9 12 7

No. of plants to

give 3 yrs

payback

Not

feasible **

Not

feasible **

Not

feasible **23 41 13




Slide 25

No. of 25k P.E. Primary & SAS satellite sites requiring installation

of dewaterers in order to provide an acceptable payback period.*



UKWIR

disposal

costs

30km

Alt.

disposal

costs

30km

UKWIR

disposal

costs

40km

Alt.

disposal

costs

40km

UKWIR

disposal

costs

50km

Alt.

disposal

costs

50km

No. of plants to

give 7 yrs

payback

6 5 5 4 4 3

No. of plants to

give 6 yrs

payback

8 6 6 4 5 4

No. of plants to

give 5 yrs

payback

13 8 9 6 7 4

No. of plants to

give 4 yrs

payback

29 13 16 9 11 6

No. of plants to

give 3 yrs

payback

Not

feasible **46

Not

feasible **18 27 11




Slide 26

Conclusions

Thickening or dewatering on 2k P.E. sites is not viable – customers should aim at

improving PST de-sludging and/or consolidation tank decanting instead (where

feasible).

Where the regional sludge reception/AAD plant already has a cake reception and

re-wetting facility:

• Disc thickening on 10,000 P.E. satellite sites (40+km) and 25,000 P.E. satellite

sites (30+km) is viable, having a payback period of ≤ 6 years and an overall

whole life cost saving of ≥ 31%.

• Screw Press dewatering on 10,000+ P.E. satellite sites is viable with a payback

period of ≤ 5-6 years for 30+km transport distances and ≤ 4-5 years for 40+km.

The overall whole life cost saving is ≥ 61%.



Slide 27

Conclusions cont.

Where a new cake reception and re-wetting facility is required to be built at the

regional sludge reception/AAD plant:

• A payback period of ≤ 7 years is possible providing a sufficient number of

10,000+ P.E. sites are upgraded to include Screw Press dewatering.

• A payback period of ≤ 4 years is possible providing a sufficient number of

25,000+ P.E. sites are upgraded to include Screw Press dewatering.

In all instances, the payback period reduces and the overall saving increases

as transport distance and P.E. increase. Actual payback periods and savings

may vary depending on the customer’s own disposal costs.



Slide 28

Acknowledgements

Martin Jolly

Richard Murray

David Robson



Slide 29

References

1) Chapman, K., Newton, J. And Van de Moortel, J., Sustainable sludge

thickening and treatment at small WwTWs, UKWIR

2) Jolly, M. and Knight, G., Commissioning Of Davyhulme Thermal Hydrolysis

Plant, 17th European Biosolids & Organic resource Conference Proceedings

3) Rawlinson, D. and Oliver. B., New Thermal Advanced Digestion plant at

Northumbrian Water’s Howdon works, 17th European Biosolids & Organic

resource Conference Proceedings

4) Wilson, S., Brown, R., Oliver, B. and Merry, J., Operational experience with

Thermal Advanced Digestion in Dwr Cymru Welsh Water, 17th European

Biosolids & Organic resource Conference Proceedings

5) Skelton, H. and Depala, P., Controlling the thickness of sludge at source,

17th European Biosolids & Organic resource Conference Proceedings

6) Tchobanoglous, G. and Burton,. F., Wastewater Engineering: Treatment,

Disposal, and Reuse, Metcalf and Eddy, Inc., 3rd Edition, McGraw Hill, Inc.

Metcalf and Eddy



Slide 30

Any questions?

Jason Sims: [email protected]

Huber Technology UK

Units C&D Brunel Park

Bumpers Farm Industrial Estate

Chippenham

Wiltshire - SN14 6NQ

Tel. +44 (0)1249 765000

Fax +44 (0)1249 449076

E-mail: [email protected]

Website: www.huber.co.uk

Thank you for your attention


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