APPENDIX 14 15 Phosphorous Removal Memo - Amazon S3 · 2020. 5. 17. · shows that the 2018 weekly influent phosphorus concentrations are much greater than the design basis weekly

APPENDIX 14.15

Phosphorous Removal Memo

3136788-45800/313678804-MEM_P removal memo.docx

20 August 2019

To Chris Mahony, Simon Perrin, Wayne Murdoch

Copy to Mark Trickey, Robbert van Oorschot

From Ben Asquith Tel +61 3 8687 8511

Subject Phosphorous removal investigation Job no. 3135258

1 Introduction GHD completed the functional design for the upgrade of the Warrnambool STP in June 2018. The upgrade was based on an agreed design basis and excluded provisions for phosphorus removal based on influent and effluent quality forecasts.

In late 2018 Wannon Water advised that phosphorus concentrations to the plant had been steadily increasing and there was a risk that the Warrnambool STP may not comply with its EPA discharge licence.

A review of trade waste data provided by Wannon Water found that the magnitude and duration of peak phosphorus loads from Warrnambool Cheese and Butter (WCB) were greater than what was adopted for the functional design. This will result in a heightened total phosphorous load on the STP and exacerbate the risk of licence non-compliance.

The purpose of this memo is to better understand the infrastructure requirements, capital and operating costs associated with total phosphorous removal at the Warrnambool STP, including the impact on solids handling. It is expected that this memo will inform discussions between Wannon Water and WCB, as well as the scope of the Warrnambool STP upgrade.

2 Phosphorous concentration design basis

2.1 Influent phosphorous concentration

A summary of influent total phosphorus concentrations adopted for the Warrnambool STP upgrade functional design (based on 2014/2015 data) and 2018 NATA data is shown in Table 1.

Table 1 Warrnambool STP upgrade – Influent total phosphorus concentrations

Scenario Weekly average TP (mg/L)

Weekday median TP (mg/L)

Weekday peak (80th percentile) TP (mg/L)

Design Basis 37.3 - 46.2

2018 No data 45.5 49.9


The data in Table 1 shows that the 2018 weekly influent phosphorus concentrations are much greater than the design basis weekly average, and the design basis peak phosphorus concentrations are now observed for most of the year. This information is also presented in the time series chart in Figure 1.

It is also noted that this analysis does not take into account the increase in phosphorous concentration that is likely to occur over weekends (due to water quality data only being available during the week) as WCB continues to discharge while MFM does not.

2.2 Effluent phosphorous concentration

The current total phosphorous median discharge limit for the Warrnambool STP is 30 mg/L.

Additionally, due to current uncertainty associated with the possibility of changes to EPA licence limits as well as future phosphorous concentration in WCB trade waste, the analysis has been expanded to also consider dosing requirements and costs to meet an effluent median limit of 10 mg/L.

2.3 Current phosphorous removal

Analysis of the influent and effluent concentration from 2014 to 2018 (refer Figure 1) revealed that the current IDEA process removes approximately 20% of the influent phosphorous. Thus, the plant is expected to be able to meet the existing median total P effluent limit of 30 mg/L if the median influent concentration is less than approximately 35 mg/L. If the median influent concentration remains greater than 35 mg/L, then year-round alum dosing for phosphorous removal would be required.


Figure 1 Influent and effluent total phosphorous concentrations at the Warrnambool STP


3 Bench scale tests

3.1 Methodology

Bench scale testing was carried out on Thursday 17 January 2019 at the Warrnambool STP. Wastewater samples were collected from the selector channel, which comprised both influent and RAS from the IDEA tanks. Wannon Water confirmed that during the sampling, trade waste customers Warrnambool Cheese and Butter and Midfield Meat were discharging to sewer.

3.1.1 Chemical phosphorous removal tests To determine the amount of phosphorous removed by alum dosing, decreasing amounts of diluted alum solution (diluted from 48 w/w% to 4.8 w/w%) were added to 2 L samples of wastewater (including no alum for a baseline comparison). Each sample was then subjected to a mixing, settling and decanting procedure that approximately mimicked the plant’s selector channel and IDEA process. Samples were rapidly mixed at 200 rpm for one minute, followed by slow mixing at 30 rpm for 30 minutes. The samples were then allowed to settle for 20 minutes before supernatant was drawn from the top of each sample. All supernatant samples were analysed for:

Total phosphorous

Soluble phosphorous

Alkalinity

pH

3.1.2 Total suspended solids tests To determine the change in total solids in the wastewater due to alum dosing, decreasing amounts of diluted alum were added to 500 ml of wastewater (including no alum for a baseline comparison). Each sample was rapidly mixed at 200 rpm for one minute, followed by slow mixing at 30 rpm for 30 minutes. The fully mixed samples were analysed for:

Total phosphorous

Soluble phosphorous

Total suspended solids

3.2 Results

3.2.1 Phosphorous removal based on alum dose Figure 2 shows the amount of total and soluble phosphorous that was measured in the supernatant after various doses of alum. It can be seen that without alum dosing, the supernatant total phosphorous concentration was 35 mg/L. Increasing the amount of alum decreased the phosphorous concentration in the supernatant. There is an approximately linear relationship between phosphorous removal down to about 5 mg/L and alum doses of up to 0.6 ml/L wastewater. Proportionally greater


amounts of alum were required to reduce residual phosphorous concentrations to less than 5 mg/L, which is consistent with literature and experience elsewhere.

Based on these results, it is estimated that approximately 20 L of alum is required to remove 1 kg of total phosphorus. This value is valid for effluent concentrations down to 5 mg/L, beyond which increasing amounts of alum would be required per kg of phosphorous. This is in addition to the phosphorous removal observed at the Warrnambool plant with no alum dosing, whereby approximately 20% of phosphorous in the influent is removed via settling in the IDEA tanks.

Figure 2 Jar testing results - phosphorous removal

3.2.2 Effect on alkalinity The test showed that alkalinity consumption was approximately 200 to 300 mg alkalinity (as CaCO3)/ml alum dosed. Due to the high initial alkalinity of approximately 970 mg/L (as CaCO3), the consumption is not expected to have a significant effect on the nitrification process in the IDEA tanks. Note that the lowest recorded alkalinity, associated with a total P concentration of 2.3 mg/L, was 655 mg/L (as CaCO3).

The pH of the effluent remained relatively stable at 8.1 to 8.2 for alum doses up to 0.2 ml/L wastewater. For alum doses ranging from 0.25 ml/L to 1.25 ml/L, the pH ranged from 8 to 7.7, with the lowest pH doses associated with the greatest alum doses.

0

5

10

15

20

25

30

35

40

0.0 0.2 0.4 0.6 0.8 1.0 1.2 1.4

Supe

rnat

ant P

(mg/

L)

Alum dose(ml/L wastewater)

Effect of aum dosing on supernatant phosphorous concentration

Total Phosphorous

Soluble Phosphorous


3.2.3 Total suspended solids The amount of TSS generated with and without alum dosing is shown in Figure 4. Total suspended solids increased approximately 16 mg TSS / mg soluble P removed. This is approximately three times greater than the theoretical value of solids generation associated with phosphorous precipitation only because it takes into account the precipitation of constituents in wastewater other than phosphorous.

Figure 3 TSS vs soluble phosphorous removed

4 Implications for the Warrnambool STP Upgrade project

4.1 Dosing and storage size

Figure 4 shows the approximate daily alum dosage and 14 day storage volume that would be required to meet a median effluent total P limit of 30 mg/L at the 2040 design flow of 27.9 ML/d. The required dosage and storage volume for a median effluent total P limit of 10 mg/L is also shown.


Figure 4 Alum dosage and storage volume required to meet effluent targets at the design flow rate (27.9 ML/d)

The alum dosage and storage volumes for the a total phosphorous influent concentration of 50 mg/L of total P concentration (as shown in Figure 4) are presented in Table 2.

It is noted that alum dosing and storage requirements are proportional to flow (for a constant phosphorus concentration). Based on a median inflow to the Warrnambool STP of approximately 15 ML/d (2018), the alum dosage and storage requirement would be approximately half of the values stated below.

Table 2 Alum dosage and storage volume required to meet design flows and loads

Influent flow (ML/d)

Influent TP (mg/L)

Effluent TP limit (mg/L)

Alum dosage (kL/d)

Storage volume (kL)

27.9 50 30 6.7 95

27.9 50 10 16.7 235


4.2 Centrifuge capacity to meet increased solids load

Table 3 shows the additional TSS generation and centrifuge operating hours based on flows and loads for 2018 and the STP upgrade design basis. Based on current (2018) flows and loads, and centrifuge operation0F

1, the solids handling plant would need to operate for an additional 6 to 8 hours per day to meet the increased solids load associated with alum dosing to achieve a total phosphorous limit of 30 mg/L (based on a five day working week).

Table 3 Additional TSS generation and centrifuge operating hours for various conditions

Scenario Influent (ML/d)

Influent TP (mg/L)

Effluent TP limit (mg/L)

Target TP (mg/L)

Additional TSS (t/d)

Additional centrifuge hrs1 (%)

2018 14.7 50 30 28 2.9 75%

10 10 7.2 190%

Design basis 27.9 50

30 28 5.5 75%

10 10 13.7 190%

Notes: (1) Increase from operation without alum dosing, based on maintaining a MLSS of 4000 mg/L

4.3 Preferred dosing location

Two alum dosing locations were considered; at the splitter box and in the selector channels. Table 4 describes the advantages and risks of each location.

Table 4 Advantages and risks of alum dosing points

Dosing point Advantages Risks

Splitter box Only one dosing line and set of dosing pumps is required.

Dosing point is close to proposed chemical storage area.

Solids may settle out in the pipework from the splitter box to the selector channels.

Potential insufficient mixing in splitter box for good floc formation.

Selector channels

Aerated selector channels provide good mixing and lower likelihood of solids settling out.

Three dosing lines and sets of pumps are required.

Considering the risk of solids settling out in the IDEA tank feed pipeline, the preferred approach is to dose alum into each selector channel. If phosphorous dosing is to be included in the Warrnambool STP upgrade, it is recommended that this location be reviewed as a value engineering exercise during the detailed design phase.

1 The centrifuge is currently (2018) operated for 12 hr/d and 5 days/week


4.4 Changes to plant infrastructure and operation

The addition of alum dosing to the overall Warrnambool STP upgrade project would require the following changes to plant infrastructure:

Alum storage area, including tanks and bunds, to be located within the proposed carbon storage area. This would allow utilisation of the proposed chemical delivery point and would require minimal (if any) modifications to roads.

Dosing infrastructure, including pumps and dosing lines

Second centrifuge and associated upgrades to the solids handling to

4.5 Preliminary cost estimate The CAPEX and OPEX associated with phosphorous dosing to achieve median total phosphorous limits of 30 mg/L and 10 mg/L are presented in Table 5. It has been assumed that an additional centrifuge would be required to achieve a limit of 30 mg/L, and two centrifuges would be required to achieve a limit of 10 mg/L. The installation of a third centrifuge would increase the likelihood of an upgrade to the plant’s power supply if the IDEA process is converted to an MBR process. However, the additional cost of this power upgrade, which would include a new transformer and main switchboard, has been excluded from the cost estimate for this case.

Table 5 Estimated additional costs associated with alum dosing at the Warrnambool STP

Effluent TP limit

(mg/L)

CAPEX OPEX (2018) OPEX (2040) NPC1,2 2040 Scope 2 emissions (t CO2-e/y)

30 $2.3 M $1.0 M $1.8 M $21.0 M 420

10 $7.0 M $2.5 M $4.5 M $51.9 M 1040 Notes: (1) NPC over the design horizon of the upgrade (i.e. until 2040)

(2) Discount rate of 3.73%


5 Key conclusions and recommendations Based on an observed increase in phosphorous concentration entering the plant in 2018, it is

recommended that the design influent total phosphorous concentration be revised to 50 mg/L.

Year-round alum dosing for phosphorous removal will be required if the median influent concentration remains greater than 35 mg/L.

We recommend that the detailed design scope for the Warrnambool STP upgrade be amended to include the following:

– Alum dosing system designed for year-round dosing (rather than trimming during peak periods) – Augmentation of the solids handling facility.

It was stated in the functional design that an upgrade to the solids handling facility should be deferred until the existing BFP reaches the end of its asset life. However, due to the increase influent total phosphorus concentration, and some uncertainty associated with the possibility of changes to EPA licence limits, it would be prudent to include the augmentation of the solids handling facility in the current design scope.

A decision by Wannon Water on whether the solids handling system requires upgrading can be deferred until the tender evaluation phase or until such time when the level of uncertainty has been reduced to an acceptable level.

It is recommended that the preliminary outputs presented in this memorandum are discussed with WCB and other trade waste customers to determine if source control (e.g. treatment at the trade waste customer site) is more attractive.

Regards

Ben Asquith Process Engineer

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APPENDIX 14 15 Phosphorous Removal Memo - Amazon S3 · 2020. 5. 17. · shows that the 2018 weekly influent phosphorus concentrations are much greater than the design basis weekly