Citizen Science - Turbidity (Part 3)

In two earlier posts, here and here, the importance of turbidity and how we measure it were discussed. In this post, I will be looking at a novel way to measure turbidity using a Hanna  Checker colorimeter designed to quantify the phosphate content of water.

Photo 1: Hanna Low Range Phosphate Checker and Cuvette

The optical layout of the Hanna Checker is basically the same as a turbidimeter (see here) insomuch as it measures the amount of light transmitted through the sample. It uses a green LED as the light source which is not ideal (white light or near infrared would be better) but you have to work with what you've got.

I did not calibrate the Hanna for turbidity using formazin standards as this is only a preliminary study. The procedure is very simple. Fill one cuvette with either distilled or de-ionised water; this represents 0 NTU. Vigorously shake the sample to be measured and fill the second cuvette (pre-washed with sample). Insert the 0 NTU cuvette and press C1 (to zero the colorimeter). Take the sample cuvette, invert five times to resuspend any sediment, place it in the cell compartment and press C2 briefly. Record the reading on the screen.

A suite of 14 river samples, collected as part of a citizen science project, with turbidities ranging from 7 NTU to 325 NTU were analysed using the Hanna Checker. The Hanna results, along with the measured turbidities by Nephelometry and Secchi Tube, are collated in Table 1.

Table 1: Hanna Phosphate Checker Readings and Measured Turbidities (NTU) using Nephelometry and Secchi Tube 

Hanna Reading	Turbidity (Nephelometer)	Turbidity (Secchi Tube)
0.01	7	<12
0.04	11	<12
0.05	14	15
0.05	19	21
0.11	26	25
0.22	56	50
0.24	41	25
0.40	69	40
0.48	74	40
0.71	134	100
0.76	122	75
1.11	221	190
1.45	228	200
1.82	325	>240

Note 1: Hanna readings are the mean of five measurements

Note 2: In Figure 2, data points with Secchi turbidities <12 NTU  or >240 NTU excluded from the linear regression analysis

Figure 1 is the linear regression plot of Nephelometric Turbidity vs Hanna Reading. The correlation is very good (R² = 0.984) over a wide range of turbidity values (7 NTU to 325 NTU). The practical range is estimated to be 15 - 400 NTU.

Figure 2 is the linear regression plot between Secchi Tube Turbidity (NTU) and Hanna Readings. The correlation is fair (R² = 0.909) over a more limited turbidity range (15 - 200 NTU) due to the lower precision and accuracy of the Secchi Tube method.

The Hanna Checker has a green LED as its light source and is, therefore, expected to show some dependence on the colour of the sample. Early results suggest this may be the case but further work is required. This method shows some promise as a technique for measuring turbidity in natural waters - albeit with a site-specific calibration.

Water Bills

 A few years ago, we switched from an unmetered potable water supply to a water meter. For the first 18 months or so, I kept a monthly check on water usage to reassure myself that everything was going to plan (i.e. lower water charges¹). Since then I've just monitored the costs on a 6-monthly basis when I receive a notification from our water company, Dwr Cymru (aka Welsh Water).

Note 1: includes sewerage charges

Photo 1: Water Meter

The supply of potable water and the treatment of sewage is, to be honest, a bit of a shambles in the United Kingdom. Prior to 1989, these services were performed by public bodies (i.e. owned and operated by the government). Under the Conservative government of Margaret Thatcher (1979 - 1990), there was a huge drive to sell off (i.e. privatise) government assets including the regional water companies.

The reasons given for selling the family silver were various and included reducing National Debt, lowering Government spending and improving efficiency through increased competition (which would lead to lower household bills). Other less palatable reasons were ideological (Margaret Thatcher was a big fan of neoliberal polices such as small government, reduced regulation and low tax), financial (cash for giveaway tax cuts), and gerrymandering (your archetypal Conservative voter is a home owner, holds investments such as stocks & shares, and wants low taxation so they can keep more of their hard-earned money).

According to Wikipedia, a total of £47 billion was raised from the sale of:

• Britoil (1982)
• Amersham Internation (1982)
• British Telecom (1984)
• Sealink (1984)
• British Petroleum (1979-1987)
• British Aerospace (1985-1987)
• British Gas (1986)
• Rolls Royce (1987)
• British Leyland/Rover Group (1988)
• British Steel Corporation (1988)
• British Rail (1993)*
• Sale of Council Houses (1979 to 2024 and beyond)**

* Conservative government with John Major as Prime Minister

** Conservative (1979-1997), Labour (1997-2010), Conservative-LibDem Coalition (2010-2015), Conservative (2015-2024), Labour (2024-)

Private financial institutions, neoliberal economists and conservative political parties will happily sing the praises of privatization . Apparently, it never fails ad everyone benefits. Certainly, some privatisations do work although they are usually in business areas where governments should only be regulators rather than owners (oil & gas, telecoms, manufacturing, etc). When it comes to public services (e.g. water, electricity, rail transport), however, dissatisfaction levels are much higher and so are the failures. The two main reasons why such public utilities fail when privatized are: (i) a fragmented industry (necessary to introduce competition) increases inefficiency and adds a huge amount of complexity (e.g. a plethora of new ticketing options in the rail industry that nobody understands and simply costs more to administer); (ii) if the privatized industry is still a monopoly - for example, I cannot choose my water company.

Anyway, back to our water bills. Before changing to a metered supply, our last unmetered annual water bill was £1,124.70 (1st April 2019 to 31st March 2020). This was an increase of £25.72 on the previous year's bill. The regulatory body for the water companies (England & Wales) is Ofwat who set the amounts by which bills are allowed to increase each year. On this (approximate) basis, I guess we would now be paying around £1,250 per year (1st April 2024 to 31st March 2025).

We pay for our metered supply by monthly direct debit. This started out at £41 per month in 2020, when the meter was first installed, but is set at only £30 per month for the coming year. On that basis, we are only paying about one quarter the amount for our water supply (and sewerage) than we would if we were still on an unmetered supply.

So I ask the question: are we especially frugal when it comes to our water usage? For the UK, the average water use is approximately 150 litres per person per day. The Dwr Cymru website provides a handy little graphic showing our average daily use (based on just two readings a year) - see Figure 1.

Figure 1: Our Daily Water Usage

We were obviously quite profligate in our water use to begin with; averaging about 165 litres per person per day. The high points in Figure 1 cover the summer months when garden watering is occasionally required. Through a number of water saving measures, we have brought this down to around 115 litres/person/day. These include: 2,400 litres of stored rainwater in water butts, using a bowl in the washing up sink to collect grey water for the garden, not flushing the loo every time, only running the washing machine and dishwasher when full, showers only, don't wash the car, jet wash the patio every 2-3 years, spot watering in the kitchen garden.

Figure 2 compares our per person use of water against a typical Welsh person.

Figure 2: Our Water Usage vs the Average Welsh Person

Despite a largish garden (and kitchen garden) to maintain, we are now below average in the amount of water we use. And the only downsides are a dirtier car and patio!

In Figure 3, our average daily water use (litres) is plotted against the Day Number since the meter was installed. A noticeable decline though possibly levelling off. Further savings will be much harder to achieve. The rationale behind installing water meters was that it would result in more efficient (i.e. less) water usage - this has been borne out empirically.

Figure 3: Decline in Water Use with Time

Smart water meters are the next planned development. In addition to providing real time usage data to the householder, they will also enable the water companies to quickly identify and fix water leaks.

Citizen Science - Turbidity (Part 2)

 In an earlier post (Citizen Science - Turbidity (Part 1)), I gave a brief introduction on why we choose to measure turbidity as part of the citizen science project monitoring pollution in the River Wye. 

Photo 1: Secchi Tube (use in upright position when filled with water!)

The majority of CSs use a Secchi Tube with a turbidity range of 12 - 240 NTU. Secchi tubes (Photo 1) are inexpensive and easy to use. Simply fill with river water until the black & white quadrants on the Secchi disc at the bottom of the tube are just no longer visible. Read off the turbidity value (NTU) printed on the side of the tube at the meniscus level. This simple procedure has low precision and accuracy because of the non-linear turbidity scale and the subjective nature of the test.

Note 1: Nephelometric Turbidity Units (NTU) are the most widely used units for quantifying turbidity and are based on 90⁰ scattering of white light (EPA Method 180.1). Formazin Nephelometric Unts (FNU) are similar (and often used interchangeably with NTU) and are based 90⁰ scattering of near infrared light (860 nm) according to the ISO 7027 method.

The only practical alternative is an optical instrument: either a turbidimeter or a nephelometer. The turbidimeter measures the amount of light passing through (transmitted by) a sample while the nephelometer measures the amount of light (usually at 90⁰ to the incident light) scattered by the particles in the liquid (Scheme 1). Turbidimeters are best suited to highly turbid fluids (> 100 NTU) whereas nephelometers work better with low turbidity fluids (< 50 NTU).

Scheme 1: Difference between Turbidimeter and Nephelometer

Professional-quality turbidimeters/nephelometers do not come cheap, typically >£1000. Fortunately, there are a range of Chinese-made instruments that are more reasonably priced for citizen science projects. The ZD2A nephelometer that I purchased is currently available for the relatively low price of £70-75 including shipping.

Photo 2: Generic Chinese Nephelometer (Model ZD2A)

My ZD2A nephelometer requires a 0.0 NTU turbidity standard and a 100 NTU turbidity standard to calibrate the nephelometer. I prepared my own nominal 0.0 NTU standard by filtering de-ionised water through a 0.22 μm membrane. The instrument came with a small bottle of 400 NTU formazin standard along with instructions for diluting to a 100 NTU standard. This is a simple dilution procedure provided you have the necessary volumetric glassware (or an accurate balance) to, for example, take a 2.5 ml aliquot and make up to 10 ml with distilled or de-ionised water. I chose to purchase a Stablcal 100 NTU standard directly to simplify the calibration procedure.

Note 2: Turbidity is calibrated using Formazin standards that have short shelf lives (from days to a few months). Stabilised Formazin Standards (e.g. Stablcal and T-CAL) have longer shelf lives (typically 1 - 2 years).

Since we have several years of turbidity data measured using Secchi tubes, one of the first tasks was to compare turbidity values measured using both techniques (Secchi vs Nephelometry). Along with a couple of fellow citizen scientists (Alan & Maggie), I collected river samples in clean 100 ml polyethylene bottles (the retention sample). To make the comparison as valid as possible, the retention samples were taken directly from the Secchi tube used to measure and record the turbidity of the river sample.

On returning home, the retention samples were analyzed using the ZD2A nephelometer. First the nephelometer was calibrated with the 0.0 and 100 NTU standards, followed by analysis of the retention samples. Retention samples were vigorously shaken for 10 seconds (to resuspend any settled particles), the sample cell was rinsed three times with sample, filled, capped, inverted 5 times and placed in the sample compartment. Turbidity readings were taken after 30 seconds, once the instrument had stabilised, and are collated in Table 1.

TABLE 1: Turbidity Values (NTU) Measured By Secchi Tube and Nephelometry
Secchi Tube (NTU)	Nephelometry (NTU)
<12	7
<12	11
15	14
21	19
25	26
25	41
40	69
40	75
50	56
75	122
100	134
190	221*
200	228*
>240	325*

Note 3: Samples with Secchi Tube values were excluded from the linear regression analysis (Figure 1)

Note 4: Samples marked with an asterisk (*) were accurately diluted by weight with de-ionised water before applying a dilution factor to the nephelometry result.

Figure 1 is the resultant linear regression analysis of the data from Table 1 (n= 11). The correlation (R² = 0.964) is better than I expected considering the relatively poor precision of the Secchi Tube method.

Despite some valid concerns regarding the accuracy and precision of the Secchi tube method, it does a remarkably good job of quantifying turbidity for this suite river samples. Further work is planned.

The Spaceguard Centre, Knighton

 On a recent visit to Knighton, we paid a visit to The Spaceguard Centre just outside the town. We had booked a tour (£10, 1½ - 2 hours) in the knowledge that the weather forecast was wet and blustery for that day (Sunday 29th September 2024). Fortunately the rain held off but being on a hill, the wind was buffeting (according to Jay Tate, a mere breeze!).

Photo 1: Two of the Three Observatory Domes

Photo 2: Third Observatory Dome

This is not your run-of-the-mill space observatory though it can still do some of that. As the name Space Guard suggests, this is the UK's contribution towards a rather important international endeavour - the detection and monitoring of asteroids and comets that are on a collision course with Earth. This could be rather catastrophic - just ask the dinosaurs!

Jay and Anne Tate, who live onsite, run this enterprise on a shoestring with no funding from the government's science budget (an absolute disgrace). They rely on tour fees and donations from visitors, including schools, revenue from a small but well-stocked gift shop, local businesses and a band of hardy and dedicated volunteers. Even then, the income only covers the running costs for the Centre - Jay & Anne are also volunteers.

The green dome (Photo 1) was built by Jay and the volunteers and will house a telescope from Cambridge University's Observatory that is surplus to their requirements. The new facility will enable The Space Guard Centre to search for Near Earth Objects (NEOs) in addition to their existing capabilities for only tracking known comets & asteroids identified by other observatories.

Please support Jay & Anne in their endeavours. Pay for a tour. Buy something from the gift shop. Make a donation. Volunteer. Your children and grandchildren will thank you for your foresight.

Halloween 2024

Photo 1: Grandchildren's Pumpkin Carving

Halloween has just passed and we didn't really notice. There were no trick or treat callers and we hadn't stocked up on sweets/candy so I've no idea what we could have given them. In the past we offered satsumas but I don't think the children were too impressed with those!

I had to pop into Hereford this morning and on my way back came across this rather splendid effort ...

Photo 2: Celebrating 'Halloween'

... someone had put in a lot of work in for just one night. Mind you, this is the same household that puts a grand display on for  Christmas ...

Photo 3: Christmas 2023

Photo 4: Christmas 2023

Photo 5: Christmas 2022

On a more serious note, how much edible pumpkin ends up as food waste? This UK survey  suggested that about 40% of the 35 million pumpkins bought in 2021 would not be eaten. I suspect this is largely down to the often messy job of extracting the pumpkin flesh and seeds through a small exit hole carved into the top or back of the pumpkin.

The next hurdle is what to do once you have separated the seeds from the flesh. The seeds can be roasted and the flesh turned into soup, bread, pie, cake, curry, hummus, and more. Pumpkin flesh is, in itself, fairly bland so you will need to add plenty of spices and flavourings. Roasted pumpkin has a better flavour but you will still need to add some flavour.

Autumn Colours at Queenswood Country Park & Arboretum

 

Photo 1: Autumn Colour at Queenswood

Once the sun had burnt off the morning mist, Saturday 26th October turned into a beautifully sunny day with crystal-clear blue skies (Photo 2) and that coolness that tells you it is Autumn.

The Ludlow Fine Book Fair was being held at Ludlow Racecourse - some 25 - 30 miles up the A49 - and Mary said she quite fancied going. In another life, she would have loved to be a professional bookbinder! We spent an hour and a half mooching round the stalls either selling fancy papers, leather hides, binding equipment, unusual books, etc and/or advertising book binding and calligraphy services. Mary spent £15 on a couple of books.

On the way back home we decided to visit the Ludlow Farm Shop (only a few minutes away) for another mooch (Photo 2). There is a large food hall, an artists' gallery, cafe/restaurant, gift shop as well as the Ludlow Distillery The Plant Centre is no longer.

Photo 2: Ludlow Farm Shop

We bought two individual pies (vegetarian) for tea and some spelt flour for breadmaking then headed off to Queenswood Country Park and Arboretum to see the autumn colours.

Photo 3: Queenswood Arboretum with the Autumn Garden in the Distance

After a cup of tea and a piece of cake (brownie), we headed off to the Autumn Garden (Photo 3) which is full of colourful acers at this time of the year.

Photo 4: Autumn Garden I

Photo 5: Autumn Garden II

Photo 6: Autumn Garden III

Photo 7: Autumn Garden IV

Photo 8: Autumn Garden V

Photo 9: Autumn Garden VI

The sun was starting to go down and we were losing the heat of the day ...

Photo 10: Autumn Sun Struggles to Light the Forest Floor

... so we headed back to the car and the short journey home. Tomorrow the clocks will be going back an hour at the end of British Summer Time - the extra hour in bed for one night does not compensate for the loss of evening light (Sunset timed for 4.51 pm the following day). Hopefully, the journey through Winter will not be a harsh one.

Photo 11: The Journey Ahead With Light at the End of the Tunnel?