Pilot Scale Trials and Financial Assessment of P-Removal Media as an Alternative to Ferric Dosing to meet P Consents at Small Works

Transcription

1 Pilot Scale Trials and Financial Assessment of P-Removal Media as an Alternative to Ferric Dosing to meet P Consents at Small Works Paul Lavender Business Development Manager plavender@aquaenviro.co.uk

2 Introduction Project Background Media products and drivers for use Laboratory Scale Trials Pilot Scale Trials Cost Benefit Analysis of Full Scale Application

3 Project Background Scottish Water is anticipating phosphorus consents for many of their small works of 1 mg/l consents based upon the Water Framework Directive integrated catchment modelling. Many of these are in soft water areas with low alkalinity which will becoming limiting to nitrification if ferric is dosed, thus necessitating caustic addition (or similar) if ferric is utilised Aqua Enviro were appointed to review P removal media based solutions as alternatives to ferric dosing.

4 Background to P Removal Media Usually porous iron containing materials using ion exchange to bind the phosphorus; Natural mineral (i.e. zeolites, ochre) Mining by-products (i.e. bauxsol) Manufactured medias (i.e. filtralite) There has been a lot of previous trial work on these medias but despite over a decade of research, P removal media is not an established solution for P removal in the water industry WHY?

5 Preliminary Media Assessment A preliminary assessment of a number of media types and pellet grades was carried out. Virotec s ViroSewage media was selected for trials based upon; High P adsorption capacity (compared to other products) Rapid P removal in preliminary lab assessment Pellet uniformity and robustness Commercial availability Recycled product ph gain issues were overcome (effluent remains <ph9)

6 Preliminary Media Assessment Virotec ViroSewage Pellets

7 Background to P Removal Media Ferric is the industry standard (high associated carbon footprint) Consumption set to rise to meet the more stringent Water Framework Directive P consents based upon the integrated catchment modelling Disproportionate increases to meet very low limits (i.e. <1 mg/l P) Is it economically viable to use media as an alternative???

8 Background to P Removal Media 22.8 kg liquid Ferric Sulphate per kg of P removed (based upon a stoichiometric dose of 1.8 and 14% Fe content. Will increase for lower consents) 71.5 kg of Virotec ViroSewage per kg P removed (based on an adsorption capacity of 14g P/kg media) 100 of liquid Ferric Sulphate per kg of P removed?? of Virotec ViroSewage per kg P removed

9 Background to P Removal Media A typical small works with a pending P consent; Bridgend WwTW s Population Equivalent x Primary Tanks 2 x Trickling Filters 2 x Humus Tanks Table 1: Bridgend wastewater analysis (dry weather spot samples)

10 Background to P Removal Media Example costs of chemical addition (provided courtesy of Scottish Water Solutions)

11 Background to P Removal Media

12 Background to P Removal Media These costs will approximately double if caustic dosing is required to address alkalinity deficiencies!

13 Laboratory Trials Multiple up-flow filters in series were used to assess a range of contact times

14 Laboratory Trials Original Media

15 Laboratory Trials Original Media

16 Laboratory Trials New Virotec ViroSewage Media Additional trials on new media at 1 hour HRT

17 Bridgend WwTW s Pilot Trial

18 Bridgend WwTW s Pilot Trial

19 Bridgend WwTW s Pilot Trial

20 Bridgend WwTW s Pilot Trial Photo: Solids in pilot plant influent (meant to be final effluent quality!) Cleaning required to maintain bed life? Air scour every few days? Full scale process must not foul best suited to works with low solids or tertiary treatment?

21 Alkalinity [mg/l CaCO 3 ] Alkalinity [mg/l CaCO 3 ] Bridgend WwTW s Pilot Trial HRT 12.5 min HRT 30 min HRT 60 min HRT 120 min HRT 240 min trials duration [d] Alkalinity Release Influent Alkalinity 300 Conclusion Elmination of ferric dosing should leave enough alkalinity for nitrification 200 but the media also releases sufficient alkalinity release to remove a further 28 mg/l NH 4 -N. 100

22 Bridgend WwTW s Pilot Trial Virotec has provided information for acid minewater applications indicating slow alkalinity release should be sustained over a number of years

23 Recycling Options Media analysed prior to use and from bed surface after the 4 week trial Data indicates that even after media exhaustion, this could be blended into a centralised sludge stream without risk of compromising EU limits for recycling to agricultural land Analysis shows leaching of sodium and calcium from the media Previous work has shown that spent media removes H 2 S from gas/air with >98% sustained H 2 S removal Potential use in odour control units or in remediation of odourous sludges?

24 Recycling Options Analyte New Media Used Media Increase EU Sludge Limits mg/kg mg/kg mg/kg mg/kg Aluminium : Dry Wt Antimony : Dry Wt <10 <10 0 Arsenic : Dry Wt Barium : Dry Wt Beryllium : Dry Wt Boron : Dry Wt Cadmium : Dry Wt <0.25 < Calcium : Dry Wt Chromium : Dry Wt Cobalt : Dry Wt Copper : Dry Wt ,000-1,750 Iron : Dry Wt Lead : Dry Wt ,200 Lithium : Dry Wt Magnesium : Dry Wt Manganese : Dry Wt Mercury : Dry Wt <2 < Molybdenum : Dry Wt Nickel : Dry Wt Phosphorus : Dry Wt Potassium : Dry Wt Selenium : Dry Wt <1 <1 0 Silver : Dry Wt <10 <10 0 Sodium : Dry Wt Strontium : Dry Wt Thallium : Dry Wt <3 <3 0 Tin : Dry Wt <20 <20 0 Titanium : Dry Wt Vanadium : Dry Wt Zinc : Dry Wt ,500-4,000

25 Cost Benefit Analysis The total costs associated with this technology are going to be dependent upon media costs so far only one-off batch production in the UK. Also, there a number of ways this could be installed i.e. 1. Utilise existing site assets such as empty sludge storage tanks, lagoons 2. Build a dedicated tank with a given asset life (i.e. 10 years). 3. Have a series of tanks in parallel with tanks being taken out of service and media replaced as it becomes exhausted

26 Cost Benefit Analysis - Example Minimum Process Size for <1mg/l SRP Consent Average current final effluent SRP concentration = 3 mg/l Design maximum SRP concentration = 4 mg/l Target final effluent SRP concentration = <1 mg/l Design HRT = >4 hours Average P removed from final effluent at 80% removal from 3 mg/l = 2.4 mg/l Average P load removed = kg/d Average final effluent P concentration after treatment = 0.6 mg/l Media bed volume required = 143 m 3 (143 tonnes of media) Media bed P removal capacity = 2,005 kg/p Media bed life based upon 14g P/kg media = 2,258 days OR 6.2 years

27 Cost Benefit Analysis - Example Process Sizing for 10 Year Asset Life Average current final effluent SRP concentration = 3 mg/l Design maximum SRP concentration = 4 mg/l Target final effluent SRP concentration = <1 mg/l Design HRT = 7 hours Average P removed from final effluent at >80% removal from 3 mg/l = 2.4 mg/l Average P load removed = kg/d Average final effluent P concentration after treatment =<0.6 mg/l Media bed volume required = 251 m 3 (251 tonnes of media) Media bed P removal capacity = 3,513 kg/p Media bed life based upon 14g P/kg media = 3,956 days OR 10.8 years Example Tank Design Tank height = 3m Tank diameter = 10.3m Pumping = from final effluent sump to 3m head Aeration = coarse bubble Control system = automated aeration scour with backwash to humus tanks, flow divert in storm conditions

28 Cost Benefit Analysis - Example Current Option Chemical Dosing Ferric dosing equipment plus telemetry Caustic dosing equipment plus telemetry Bunding Safety showers Tanker turning area CAPEX = k Alternative Option ViroTec Media 250 tonnes media at 500* per tonne = 125k Concrete slab and tank = 70k Aeration grid and blower = 40k Telemetry and control systems = 20k CAPEX = 265k *Media costs for this trial were in excess of 500 per tonne but this figure has been used based upon an assumption that development of a market for this media within the wastewater sector in the UK will lead to cost reductions. The actual media cost will be a critical factor and Optional Sump for Alkalinity Return Sump and submersible pump with flow control = 30k

29 Cost Benefit Analysis - Example In this example the Virotec media is a cost effective alternative to ferric and caustic addition but not for ferric only. The ability to utilise existing assets for the media and/or media costs may alter this balance.

30 Conclusions Virotec s ViroSewage media appears to be a potentially cost effective alternative to chemical addition at very small treatment works where the capital and maintenance costs of chemical addition are disproportionally high The greatest potential benefit is on soft water areas where alkalinity is lacking and removing the need for ferric dosing also means caustic addition is not required The economics will be influenced by site specific factors such as whether any existing assets can be utilised Solid accumulation within the media as well as bio-fouling pose a very significant risk. A low solids feed is required and provision for media bed cleaning will need to be made (i.e. coarse air scour)

31 Conclusions The risks associated with pellet integrity, bio-fouling, blockages and scouring requirements will be better understood with longer term operational experience The media has the potential to be recycled back to agricultural land although the spent media has been shown to have a high affinity for H 2 S and could be used in odour control applications The cost of the media will be a key factor in technology uptake and this represents the greatest proportion of the cost associated with this technology

32 Acknowledgements Aqua Enviro would like to thank Scottish Water and Virotec for their help with this study, especially; Graeme Moore Scottish Water Andy Pitt Scottish Water Solutions Chris Purves Scottish Water Steven Young - Virotec