Anaerobic wastewater treatment plants often encounter nutrient-related problems. A common pain point for anaerobic wastewater treatment plants is the formation of struvite, also known as MAP (magnesium ammonium phosphate hexahydrate). Struvite is a phosphate material (NH4MgPO4·6H2O) and is likely to form in an environment, where there is higher conductivity, lower temperatures, high pH, and higher concentrations of magnesium, ammonia, and phosphate, all of which can be found during the anaerobic digestion of sludge.

Struvite scale accumulation in an anaerobic wastewater treatment plant can lead to great inefficiency within the plant or operation, due to the clogging of the pipes, pumps , and equipment. Some solutions to remove struvite scale include pipe replacement, hydro-jetting or the use of a mechanical grinder. An issue with the above mechanical solutions is that many lines can be underground which requires significant downtime. Another way to clear the system of struvite buildup is with Chemical cleaning. Chemical cleaning products such as CED struvite remover have been developed to remove and prevent struvite with minimal downtime. However, the chemicals and man-hours expended to maintain equipment effected by struvite can be very costly. Depending on the size of the facility, the cost of treating struvite can range from $15,000-400,000/year.

Recently, an innovative chemical-free option has been introduced to the municipal anaerobic wastewater sector. This chemical-free, electric method of removing and preventing struvite has been developed and tested successfully at anaerobic wastewater treatment plants in the USA. The electronic sinewave it produces is induced throughout the water in the pipes, pumps, and equipment, it is, therefore, effective on underground piping as well. One such successful and award-winning product is HydroFLOW water conditioning devices, powered by the unique and patented Hydropath technology.

When installed in accordance with the manufacturer’s recommendations, the HydroFLOW physical water conditioning devices, prevent struvite from accumulating as hard scale and can assist in the removal of existing struvite deposits. It is important to note that constant liquid flow is required in order to remove hard scale deposits from a system.

The HydroFLOW devices induce a unique frequency (i.e. the Hydropath signal) into the liquid medium which causes the component ions that makeup struvite MAP (NH4MgPO. 6H2O) to come together as loosely held together clusters; the presence of the Hydropath signal is believed to induce the formation of these clusters. When certain conditions are created (i.e. pressure change, temperature change, turbulence, etc.) the clusters precipitate out of solution and form stable crystals of struvite that remain in suspension. These TSS particles are believed to be roughly 5-10 microns in size. The stable crystals are not able to adhere to surfaces as hard scale and are carried away with the flow or can be filtered out of a system. In some cases, a small quantity of material is left behind and forms a soft and thin layer of substance that has negligible impact on liquid flow inside pipes and equipment.

Struvite formation from the magnesium, ammonium and phosphate ions does not accumulate uniformly throughout a piping system, but rather at different points according to a variety of factors. This means some ions remain in solution and may precipitate down the line. The HydroFLOW device will assist in the creation of crystals that typically do not decompose when the signal is not present.

 

For additional data and example of how the HydroFLOW devices remove and prevent struvite please see the below third-party verification that was conducted in partnership with Jacobs engineering (Ch2m) at an anaerobic wastewater treatment plant in Colorado.

 

 

 


T E C H N I C A L M E M O R A N D U M

Third-Party Technology Verification of the Hydropath

Technology at the Robert W. Hite Treatment Facility, Denver, Colorado

 

PREPARED FOR: Tal Journo/HydroFLOW USA LLC (HydroFLOW USA)

PREPARED BY: Samuel Jeyanayagam, PhD, PE, WEF Fellow/CH2M HILL, Inc. (CH2M)

DATE: 27 September 2017

Scope and Purpose

The primary objective of this independent, third-party technology verification is to validate the effectiveness of the HydroFLOW I Range product with respect to controlling struvite scaling at selected test sites. The verification is based on a review of sampling data, visual observations, and discussion with plant staff, and focuses on identifying changes to struvite scaling before and after installing HydroFLOW units. During the testing period, no effort was made to investigate the mechanism that allows HydroFLOW units to prevent scale accumulation. HydroFLOW USA intends to examine the mechanism in 2018.

This technical memorandum specifically discusses the verification testing completed at the Robert W. Hite Treatment Facility (RWHTF) in Denver, Colorado, and the observed outcome.

Technology Description

The HydroFLOW I Range uses Hydropath technology. When properly installed on a pipe (see Figure 1), it induces a 150 kilohertz, oscillating sine wave, alternating current (AC) signal. The electric induction is performed by a special transducer connected to a ring of ferrites. The pipe and the flowing fluid act as a conduit, which allows the signal to propagate. The induced AC signal is believed to cause the mineral ions that makeup struvite (magnesium, ammonium, and phosphate) to form loosely held together clusters. When certain conditions are created (e.g., pressure change, temperature change, and turbulence) the clusters precipitate out of solution and form stable crystals of struvite that remain in suspension and are not able to adhere to surfaces as hard scale; the crystals are carried away with the flow. Because hard scale no longer accumulates, the shear forces created by the flowing liquid erode and soften existing scale deposits over time. It is important to note that constant liquid flow is required to remove hard scale deposits from a system.

 

 

 

 

Figure 1. Typical HydroFLOW Unit Installation

Robert W. Hite Treatment Facility Description

The RWHTF (see Figure 2), is owned and operated by the Metro Wastewater Reclamation District in Denver, Colorado. The RWHTF was constructed in 1966, is rated at 220 million gallons per day (mgd) and is the largest facility in the Rocky Mountain West region. The RWHTF treats, on average, 135 mgd for a service population of more than 1.8 million people.

 

 

Figure 2. The Robert W. Hite Treatment Facility

The RWHTF has two liquid stream train plants (north and south) each consisting of screening, grit removal, primary clarification, activated sludge basins configured to achieve nutrient removal, secondary clarification, and disinfection. The primary sludge and waste-activated sludge (WAS) from the two plants are combined and processed in a single solids stream that includes gravity thickening for primary sludge, dissolved air floatation thickening for WAS, two-stage anaerobic digestion, centrifuge dewatering, and land application of Class B biosolids.

Scale accumulation that is believed to be a combination of struvite and other amorphous mineral deposits occurs at certain locations, especially in the centrate and digester piping.

Test Details

The Metro Wastewater Reclamation District (MWRD) and HydroFLOW USA signed a memorandum of understanding to participate in a 60-day product evaluation test at the RWHTF to determine the effectiveness of the Hydropath technology in mitigating scale formation.

In addition, a site-specific test protocol was jointly developed by CH2M, MWRD, and HydroFLOW USA that outlines details of the tests. The test protocol provided a consistent framework and guidance for testing so that the results could be used for the third-party technology verification by CH2M. Seminal information from the protocol is presented in the following sections.

Test Period

The test period was agreed to be for 60 days, with a provision to negotiate an extension, if desired by the RWHTF. Testing began 1 March 2017.

HydroFLOW Unit Installation

As shown on Figure 3, the plant’s centrate conveyance system consists of the following components:

•Centrate piping (8-inch, glass-lined, ductile iron)

•Foam tank

•Transfer pump

•Centrate holding tank

 

 

 

 

Figure 3. HydroFLOW Unit Locations and Sampling Points

From the operating centrifuges, centrate flows to the foam tank before being pumped to the centrate holding tank. There are two centrate transfer pumps (one duty pump and one stand-by pump). The duty transfer pump was used to determine the impact of the HydroFLOW units. Centrate is transferred continuously, 24 hours per day, everyday.

HydroFLOWunits were installed at two locations (see Figure 3).

HydroFLOW Unit 1: Suction side of the transfer pump

HydroFLOW Unit 2: Discharge side of the transfer pump, between HydroFLOW Unit 2 and the centrate holding tank

Sampling Locations

According to RWHTF staff, three primary sampling locations have been identified (see Figure 3):

1.Sampling Point 1: Upstream from the foam tank

2.Sampling Point 2: Suction side of the transfer pump

3.Sampling Point 3: Upstream from the centrate holding tank

Baseline Condition

Before activating the HydroFLOW units, baseline information was gathered at the transfer pump and the pump discharge pipe at a location upstream of the second HydroFLOW unit. The baseline information characterized the extent of scaling and included thickness and other visual observations, photographs of the scaled surfaces, and samples of the scale. To observe scale accumulation trends, a portion of the scaled surface was cleaned before energizing the HydroFLOW units.To fully assess the effectiveness of the Hydropath technology, the addition of dilution water to the foam tank was discontinued during testing.

Sampling and Analysis

Weekly samples were collected from the three sampling locations and analyzed for the following parameters:

•Soluble ions (magnesium, potassium, sodium, calcium, and iron)

•Total ions (magnesium, potassium, sodium, calcium, and iron)

•Ortho-phosphate

•Total phosphorus

•pH

•Ammonium

•Conductivity

In addition, visual observations were noted and photographs taken of the transfer pump and pump discharge pipe surfaces, as shown in Table 1. This was done three times at the transfer pump, but only twice at the pump discharge pipe, because of the inability to isolate the centrate pipe.Table 1. Visual Observation of Scale Accumulation

 

Action

Pump Suction

Pump Discharge Pipea

When Performed

Start (baseline), Middle, and End of Testing

Start (baseline) and End of Testing

Visual Observation

X

X

Scale Thickness Measurement

X

X

Photographs

X

X

a Upstream from HydroFLOW Unit 2

Results

Review of Sampling Data

A good indication of struvite formation is the change in soluble concentrations of its key constituents: magnesium, ammonium, and phosphate (ortho-phosphate). As shown on Figures 4, 5, and 6, these parameters did not exhibit any appreciable change between Sampling Points 1 and 3 during the sampling period (1 March through 26 April 2017), which implies there was no struvite formation or scaling.

 

Figure 5. Ammonium Concentration Profile

 

 


Figure 6. Ortho-phosphate Concentration Profile

 

The variation in data is due to systematic and random errors. Systemic errors may be due to an imperfectly made instrument or to the personal technique and bias of the observer. Random errors are due to unknown causes and usually follow the laws of chance. Averaging the data will resolve some of the errors.

A review of the average values over the sampling period (see Table 3) shows that although concentrations and pH were favorable for struvite formation, this did not occur and the concentration profiles of the three soluble components remained relatively flat at the three sampling points. If struvite formation had occurred in the test segment, soluble concentrations would have declined between Sampling Points 1 and 3.

Table 3. Average Concentrations of Struvite Constituents and pH Values

Parameter

Upstream from Foam Tank (Sampling Point 1)

Pump Suction (Sampling Point 2)

Upstream from Holding Tank (Sampling Point 3)

Soluble magnesium, mg/L

9.05

8.08

7.15

Ammonium, mg/L

1,143

1,028

1,117

Ortho-phosphate, mg/L

235

196

222

pH

8.1

8.0

8.0

Note:

mg/L = milligrams per liter

The full dataset provided in Attachment 1 shows that the concentration profiles of other measured constituents also remained relatively flat.

Visual Observations

The RWHTF staff made visual observations and took photographs of the scale formation before activating and after energizing the HydroFLOW units. The “before” observations represent the baseline condition and provide a basis for making a qualitative determination of the effectiveness of the HydroFLOW units. Two locations that typically experience nuisance scaling were targeted for this comparison: (1) the transfer pump and (2) the pump discharge pipe.

The baseline condition for the transfer pump (photograph dated 27 Sept 2016 in Figure 7), shows heavy struvite encrustation, which typically causes plant operators to take the unit offline for acid cleaning twice a year. The photograph dated 27 April 2017 shows softer and thinner scale that can be easily wiped off.

 





 

 

-Figure 7. Before and After Photographs of the Transfer Pump

 

The before and after photographs of the pump discharge pipe between the transfer pump and second HydroFLOW unit are shown on Figure 8. The “before” photograph dated 27 Sept 2016 shows heavy scaling and reduced pipe inside diameter. The photograph dated 1 March 2017, before the test, shows the section of hard struvite that was cleaned to expose the green, glass-lined pipe. The “after” photograph, dated 27 April 2017 shows the following:

•Some of the hard struvite had been gradually removed to further expose the pipe.

•The remaining struvite scale had become softer and thinner.

 

area

 

before test

 

Figure 8. Before and After Photographs of the Transfer Pump Discharge Pipe

 

In general, RWHTF staff reported the following observations at the transfer pump and discharge pipe locations:

•Before the test, the scale was thick (approximately 1/8 inch), hard, and greyish in color. It was possible to collect large pieces of hard scale.

•Sixty days into the test, the scale was softer and thinner, with some areas of the surface becoming visible. The scale samples broke into smaller pieces.

•At the end of the test, the scale was significantly thinner, making it impossible to collect a scale sample. An increasing amount of surface was exposed.

Conclusion

The centrate conveyance the system at the RWHTF, particularly the transfer pump and pipe, experience scaling, which requires that the system be periodically taken offline for cleaning. Two units of the HydroFLOW I Range were installed on the centrate line to evaluate their effectiveness in controlling scaling. Targeted sampling during the 60-day test period included sample collection and analysis and observations of scale characteristics before and after the HydroFLOW units. Based on the review of the data and discussion with RWHTF staff, the use of HydroFLOW I Range on the centrate line was effective in softening the existing scale and preventing the formation of new scale. Softening of the existing scale allowed a substantial portion of the original hard scale to be removed during the 60-day test period, because of the shearing the action of the flowing liquid.

This technical memorandum verifies that the use of HydroFLOW I Range units at the RWHTF prevented scale formation in the centrate transfer pump and pipe. The HydroFLOW units also caused changes in the characteristics of the existing scale, making it easy to be removed by the flowing liquid. It should be noted that following the test, RWHTF purchased and installed four HydroFLOW units on the centrate and digested sludge lines.

Disclaimer

This technical memorandum is not a global validation of HydroFLOW I Range and provides no assurance that it will be successful in mitigating scaling at other water resource recovery facilities. CH2M recommends that other facilities interested in using HydroFLOW units to mitigate scale formation, conduct onsite testing to validate its effectiveness under plant-septic conditions. Such tests are valuable in demonstrating the technical and financial feasibility of implementing HydroFLOW. CH2M understands that HydroFLOW USA has a limited number of rental units that it uses for trials. The availability of the rental equipment should be discussed directly with HydroFLOW USA.

Acknowledgment

This technology verification was made possible through the assistance of Edyta Stec-Uddin/RWHTF and Jim McQuarrie/RWHTF, who were involved in data collection and overall coordination. Heat Waves Water Management LLC (the regional HydroFLOW USA representative) provided and installed the test units. This study was funded by HydroFLOW USA and Hydropath Technology, Ltd.

 

Summary Data

Attachment 1. Summary Data

Date

(d/m/y) 

Upstream from Foam

Tank

Pump

Suction 

Upstream from

Holding Tank

Upstream from Foam

Tank

Pump

Suction

Upstream from

Holding Tank

Upstream from

Foam

Tank

Pump

Suction

Upstream from

Holding Tank

Upstream from Foam

Tank

Pump

Suction

Upstream from

Holding Tank

Upstream from Foam

Tank

Pump

Suction

Upstream from

Holding Tank

Upstream from Foam

Tank

Pump

Suction

Upstream from

Holding Tank

Upstream from

Foam

Tank

Pump

Suction

Upstream from

Holding Tank

Upstream from

Foam

Tank

Pump

Suction

Upstream from

Holding Tank

pH

pH

pH

Conductivity 

Conductivity 

Conductivity 

Ammonia 

Ammonia 

Ammonia 

Orthophosphate 

Orthophosphate 

Ortho- phosphate 

Total

Phosphorus 

Total

Phosphorus 

Total

Phosphorus 

Dissolved Calcium

Dissolved Calcium

Dissolved Calcium

Dissolved Iron

Dissolved Iron

Dissolved Iron

Dissolved Potassium 

Dissolved Potassium 

Dissolved Potassium 

3/1/17

8

7.9

8.1

9020

8220

8420

1120

1040

1090

266

246

241

275

267

271

40.7

27.5

27.3

0.153

0.133

0.136

273

258

259

3/8/17

8.2

8

8.1

8240

8940

9080

1120

1150

1130

215

220

229

37.4

31.9

30.3

0.118

0.124

0.136

254

261

262

3/15/17

7.9

7.9

7.9

9090

8500

8700

1180

1070

1100

327

185

283

230

38.1

27.7

27.7

0.215

0.162

0.196

269

237

240

3/22/17

8

7.9

7.9

8680

8460

8870

1290

1230

1250

213

195

203

227

232

227

38.6

33.7

32.3

0.169

0.14

0.155

267

243

250

3/29/17

1190

1070

1130

201

177

193

201

189

40

34.2

35.4

0.133

0.125

0.123

242

223

229

4/5/17

8.2

7.8

8.1

8770

3710

9000

1140

430

1160

205

71.7

210

219

72.7

42.3

34.4

36.9

0.158

0.133

0.145

246

95.5

245

4/12/17

8

8

8

8610

9240

9010

1060

1210

1080

212

233

215

212

262

35.3

27.6

26.5

0.126

0.157

0.189

246

279

258

4/19/17

8.2

8.1

8

8430

6550

8490

1090

1080

1130

232

219

204

241

234

242

42.5

39

36.7

0.184

0.154

0.166

260

272

280

4/26/17

8

8

8

8920

8000

8120

1100

973

985

242

213

218

251

230

230

40

34.7

34.9

0.167

0.109

0.114

285

247

253

Average

8.1

8.0

8.0

8720

7703

8711

1143

1028

1117

235

196

222

232

215

243

39

32

32

0.158

0.137

0.151

260

235

253

 

Date

(d/m/y) 

Upstream from Foam

Tank

Pump

Suction

Upstream from

Holding Tank

Upstream from Foam

Tank

Pump

Suction

Upstream from

Holding Tank

Upstream from

Foam

Tank

Pump

Suction 

Upstream from

Holding Tank

Upstream from Foam

Tank

Pump

Suction 

Upstream from

Holding Tank

Upstream from Foam

Tank

Pump

Suction

Upstream from

Holding Tank

Upstream from Foam

Tank

Pump

Suction

Upstream from

Holding Tank

Upstream from

Foam

Tank

Pump

Suction 

Upstream from

Holding Tank

Dissolved

Magnesium 

Dissolved

Magnesium 

Dissolved

Magnesium 

Dissolved Sodium

Dissolved Sodium

Dissolved Sodium

Total Calcium

Total Calcium 

Total Calcium

Total Iron

Total Iron

Total Iron

Total Potassium 

Total Potassium 

Total Potassium 

Total

Magnesium 

Total

Magnesium 

Total

Magnesium 

Total

Sodium

Total

Sodium 

Total

Sodium

3/1/17

9.76

7

10

106

102

106

38.3

49.4

37.9

0.81

11.7

6.55

264

238

250

11

11.1

11.3

106

100

103

3/8/17

9.58

7.15

7.69

109

109

109

43.7

55.2

152

4.38

7.07

33.3

258

270

284

15.7

13

11.4

118

117

121

3/15/17

10.6

6.54

6.67

107

105

106

45.8

100

117

4.24

38

46.9

261

247

255

13

17.5

19

112

115

115

3/22/17

7.43

8.49

7.41

108

108

107

46.4

49.2

93.9

5.35

8.89

24.4

250

237

247

11.2

11.4

18.7

103

105

105

3/29/17

7.77

8.87

9.27

104

106

104

54.1

56.1

34.9

4.64

8.46

0.679

239

226

216

19.8

16.2

13.4

105

108

101

4/5/17

8.84

13

6.85

103

100

106

43.3

34.6

41.5

0.891

0.249

0.951

244

95.7

240

11.9

13.6

11.9

107

99

107

4/12/17

7.16

4.82

3.44

107

109

109

53.9

99

200

6.98

34.7

81.5

237

271

269

12.9

16.2

28.7

102

104

108

4/19/17

10.4

8.16

6.14

105

105

107

40.2

53.3

3.2

5.76

258

267

11.2

15.3

103

104

4/26/17

9.95

8.68

6.91

111

107

110

38.1

42.9

35.8

0.678

2.67

1.06

274

239

243

10.7

11.7

10.1

106

104

105

Average

9.05

8.08

7.15

107

106

107

45

59

85

3.50

12.77

22.34

253

231

252

13

14

16

107

106

108