Filtration, disinfection and water management

Filtration, disinfection and water management

From recognition of pollution and selection of equipment to capacity calculations, monitoring and operation plan

Water is the main visible element in the fountain. Its quality affects the transparency of the effects, the performance of the nozzles, the durability of the equipment, the cleanliness of the surfaces and the experience of the visitors. In interactive fountains, water quality is directly related to the health of users.

Clear water is not necessarily microbially suitable. Also, installing a filter alone does not provide disinfection. Water quality management requires a coordinated set of hydraulic design, particulate removal, chemical control, disinfection, cleaning, and monitoring.

In this chapter, a distinction must be made between two issues: the equipment that treats water and the program that maintains the proper functioning of that equipment over time. The project needs both.

Numbers and calculations are examples of this educational chapter. The final limits of water quality and operating conditions should be determined based on the type of use, local authority requirements and equipment specifications in the project documents.

25–1. The first decision: is the fountain decorative or interactive?

Choosing a treatment system should start from the type of contact people have with water.

The title of the project alone is not decisive. If children are playing in a ostensibly decorative water feature, simply installing a sign will not solve the issue of water quality and type of exposure.

In the collection of urban fountains introduced on the GSO website, different arrangements can be seen such as musical, dry floor and floating fountains. The treatment plan should be prepared based on the actual application of each project. Urban Fountains Group - GSO ^[160]

25–2. What pollutants enter the fountain?

Sources of pollution can be analyzed in four groups:

Suspended particles and substances: dust, leaves, sand, fibers and particles from traffic.

Organic matter: plant remains, bird droppings, substances transferred from the body of users and some detergents.

Soluble substances: compensatory water solutes, compounds obtained from injecting substances and substances imported from the environment.

Microbial fouling and biofilm: Microorganisms and sticky films that form on wet surfaces, tanks and network components.

Each group needs a different answer. The mesh can capture the leaf, but it does not remove dissolved solutes. A particulate filter can improve clarity, but is not a substitute for a disinfection system.

Pentair also states in its sand filter manual that removing suspended solids is different from water disinfection. Pentair THS sand filter guide ^[161]

25–3. Inlet water testing and design basis determination

Before choosing the equipment, the quality of the water supply source should be known. The initial review, depending on the source and type of project, can include the following:

• pH and alkalinity;

• Hardness and dissolved solutes;

• electrical conductivity;

• turbidity and suspended matter;

• iron and manganese, if possible;

• Chloride and other factors affecting corrosion;

• Microbial quality according to the type of use;

• Ultraviolet transmission, if UV is selected.

City water, wells and alternative sources cannot be considered equivalent to each other without investigation. The quality of the resource may also change in different seasons.

The design basis sheet should specify: what is the incoming water quality, how is the target quality defined and which process is responsible for controlling each parameter.

In the project with direct contact, the decision about the permission of the water source should be clarified with the competent authority before purchasing the equipment.

25–4. Purification steps and the task of each step

A system can be a combination of the following steps:

OASE also introduces filtration, skimmer and chemical treatment as equipment groups in the water quality department. The choice among these equipments should be made according to the application of the project. Water quality equipment - OASE ^[162]

In interactive fountains, the sequence and connection of the steps is of particular importance. A small UV in the side circuit does not necessarily provide disinfection of all water splashed towards users.

Figure note from the source manuscript

Figure 25-1 instead

Suggested image: conceptual diagram of water quality management steps, showing garbage collection, filtering, chemical control, disinfection and monitoring. The demonstration circuit and the filtration circuit should be displayed separately and the water disinfection route should be clear before reaching the users.

Caption: "Each stage is responsible for controlling part of the water quality; "Equipment selection should be done along with determining the flow path."

25–5. circulation time; Its concept and limitations

The nominal circulation time is the time required for a volume equivalent to the base volume of the system to pass through the purification circuit:

$T=\frac{V}{Q_f}$

or:

$Q_f=\frac{V}{T}$

In these relationships:

• $V$: Volume of calculation base, cubic meters;

• $Q_f$ : actual flow of filtration, cubic meters per hour;

• $T$ : nominal circulation time, hours.

The base volume must be defined in the design and the effective volume of the related components, according to the selected reference, should be included in it.

A nominal circulation does not mean that all water particles pass through the filter. In a fully mixed tank, some of the water has passed through the circuit several times and some has never passed through the circuit.

To demonstrate this concept, in the hypothetical model of complete mixing with 100% removal of one pollutant in each pass and without the introduction of new pollutant:

$\frac{C(t)}{C_0}=e^{-Q_{f}t/V}$

After a circulation time, about 36.8% of the original amount remains. This simple model does not guarantee microbial performance; It only shows the limitation of the concept of "one time circulation".

Improper placement of input and output and the presence of low flow points can also make the actual performance weaker.

25–6. Calculation example of selection of filtration capacity

Consider a hypothetical interactive fountain with a base volume of 12 cubic meters.

For this example, a circulation time of 30 minutes is selected. CDC operating guidelines for interactive water features recommend a run time of 30 minutes or less; This value should not be generalized to all decorative fountains without investigation. Manual for using interactive fountains - CDC ^[163]

$Q_f=\frac{12}{0.5}=24m^3/h$

Now let's assume that the filtration design rate for the selected filter and bed, after technical review, is set at 25 cubic meters per square meter per hour. This is the assumed number of the example.

Required level:

$A_f=\frac{Q_f}{v_f}$

$A_f=\frac{24}{25}=0.96m^2$

If two parallel filters with an effective bed diameter of 0.80 m are checked:

$A_{total}=2\times \frac{\pi (0.8{)}^2}{4}\approx 1.005m^2$

Actual filtration rate:

$v_f=\frac{24}{1.005}\approx 23.9m/h$

Therefore, in terms of substrate level, this option is consistent with the assumption of the example. Final approval depends on bed depth and type, filtration quality, pressure drop, manufacturer's allowable capacity, and project requirements.

Two parallel filters do not automatically support each other. If the entire flow passes through a filter:

$v_f=\frac{24}{0.503}\approx 47.7m/h$

This situation should be investigated separately; It may be necessary to reduce the capacity or stop general use when a filter is removed from the circuit.

25–7. Filter washing and actual pump capacity

For a backwashable filter, the design does not end with the filtration flow rate. The pump, tank and disposal line must also provide washing conditions.

In the continuation of the example, let's assume that the manufacturer of the selected substrate has approved the washing rate of 40 meters per hour and the duration of 4 minutes for certain conditions.

For a filter:

$Q_{bw}=v_{bw}A$

$Q_{bw}=40\times 0.503\approx 20.1m^3/h$

Volume of water for the washing step:

$V_{bw}=Q_{bw}\frac{t}{60}$

$V_{bw}=20.1\times \frac{4}{60}\approx 1.34m^3$

To wash two filters separately, this step consumes about 2.68 cubic meters of water. Water for rinsing and other uses must be added separately.

The Pentair guide emphasizes on providing a suitable washing flow rate and sufficient capacity of the disposal line; Its rate and duration depend on the model and platform. Filter reverse washing - Pentair

The filter pump should also be checked both in the clean filter condition and close to the clogging limit. Increasing the drop can reduce the flow rate and lengthen the actual circulation time.

Figure note from the source manuscript

Figure 25-2

Suggested image: filter section in reverse filtration and washing mode, along with flow direction and bed expansion space. Next to it, insert a small table of example calculations.

Subtitle: "Filter surface, washing flow rate and water disposal capacity must be designed at the same time."

25–8. Primary disinfection and limits of exploitation

In chlorine based system, three concepts should be clear:

• Free chlorine: measurable part of free chlorine in water;

• Combined chlorine: compounds created by the reaction of chlorine with some pollutants;

• Total chlorine: sum of free and combined chlorine.

The smell of water is not a measure of chlorine. The amount of free chlorine and pH should be measured by the appropriate method.

For example, CDC guidelines for interactive water fountains state:

These numbers are minimums and guidelines for a specific reference; The full allowable range, concentration ceiling and project set point should be determined by local regulations and equipment limitations. Mentioning the state with cyanuric acid is not a general recommendation to add it. Limits and monitoring of interactive water fountains - CDC

For decorative fountains, the disinfection program should be developed according to the risk assessment of the same system.

25–9. UV and secondary disinfection

UV should be selected based on proven performance; The rated power of the lamp alone does not determine the disinfection capacity.

The selection parameters are:

• The highest flow rate;

• Lowest expected ultraviolet transmittance or UVT;

• The target microorganism and the level of inactivation required;

• End-of-life state of the lamp and contamination of the sheath;

• Validity range of the test and device monitoring system.

Xylem explains that the capacity of a reactor can change significantly as the UVT changes, and performance should be checked within the validated range. UV also does not create a protective disinfectant residue in the pond water. Selection and utilization of UV in water spaces - Xylem ^[164]

Specific CDC guidance for interactive fountains suggests secondary disinfection with at least 99.9% reduction of infective Cryptosporidium oocysts per pass and treatment of all water before reaching users. Guide to the design and management of interactive fountains - CDC ^[165]

Therefore, if in the previous example the filtration flow rate is 24 m3/h, but the maximum flow of the display path is 60 m3/h, the secondary disinfection unit of the display path should be checked for the same flow rate and water quality.

This difference should be clear on the map. The failure of the secondary unit should also have a defined behavior so that the flow does not reach the users without the necessary conditions.

25–10. Legionella biofilm and risk management

Biofilm forms on wet surfaces and may remain in the tank, behind parts, inside low-flow pipes, and around nozzles. Increasing the amount of disinfectant, without cleaning and correcting the inappropriate spots, does not always solve the problem.

In the Guide to Decorative Fountains, the CDC identifies sediment and biofilm, temperature, water retention, and disinfectant residual as important factors in Legionella control. This guide emphasizes a water management plan, avoiding long stoppages and regular cleaning. Legionella control in decorative fountains - CDC ^[166]

Design measures include access for cleaning, drainability, reduction of stagnant paths and consideration of water heating agents. Turning off the display should not lead to a drop in water quality.

If an associated illness is suspected or a test result is worrisome, the response should be coordinated with the health official and the approved program. Reopening based on apparent water clarity is not sufficient.

25–11. Control of deposition, corrosion and solute accumulation

Evaporation removes water from the system, but most of the non-volatile solutes remain in the water. Therefore, the continuous addition of compensation water can be associated with an increase in the concentration of some soluble substances.

To choose a solution, the difference between these processes must be clear:

• The particle filter does not normally remove the hardness of the solution;

• An ion exchange hardener is not the same as an extensive solute removal system;

• Reverse osmosis requires pre-treatment and management of the concentrated stream;

• Anti-fouling additive is not a license to ignore water balance and its chemistry.

Sedation control should be coordinated with pH, alkalinity, hardness, temperature and equipment type. Lowering the pH excessively to prevent fouling may damage materials or equipment.

For a fountain with plants or fish, the choice of disinfectant or algaecide must be checked separately. A suitable product for a non-aquatic decorative pond is not necessarily suitable for a biological pond or water play area.

25–12. Material injection and automatic control

The injection system must work according to the actual water load. The volume of the tank alone does not determine the daily consumption of the substance; Light, temperature, incoming pollution, number of users and chemical reactions are also effective.

To understand the difference between "theoretical value" and "actual consumption", the following relationship is used:

$m=\Delta C\times V$

If $\Delta C$ is in milligrams per liter and $V$ is in cubic meters, then $m$ is in grams.

For a volume of 12 cubic meters and a theoretical increase of 1 mg/liter:

$m=1\times 12=12g$

This number is the theoretical mass of the effective substance based on a certain concentration and without considering chemical consumption; 12 grams is not considered a commercial product or injection prescription.

In the design of the control, the interruption of injection when there is no flow, the limitation of continuous injection, the warning of sensor failure and the prevention of uncontrolled injection should be foreseen.

OASE in the Clear Fountain system combines pH and ORP control with injection equipment. This example shows the application of automatic control; The configuration of each project should still be specific. Clear Fountain System - OASE ^[167]

25–13. The difference between ORP and chlorine measurement

ORP, or oxidation-reduction potential, is expressed in millivolts and is affected by the combination of oxidizing and reducing substances in water.

ORP is not a direct measurement of free chlorine concentration. Converting a fixed ORP number to a fixed chlorine value is not reliable for all waters. Hach also explains the effect of pH, temperature, and other compounds on this relationship. ORP limitation in chlorine estimation - Hach ^[168]

Therefore, the use of ORP for control should be accompanied by an independent measurement method of the required parameter.

In a monitoring program, sensor condition is also important: calibration, cleanliness, sample flow rate, response time, and sample collection location must be monitored. A stable number on the display does not necessarily mean the measurement is correct.

Figure note from the source manuscript

Figure 25-3 instead

Suggested image: Photo of monitoring panel including pH sensor, ORP, chlorine measurement and sample path. Beside it, a comparative manual test by the operator should be displayed. The title of each sensor should be written based on the actual equipment.

Caption: "Automatic monitoring should be supported by independent measurement and sensor accuracy control."

25–14. Monitoring and corrective action plan

In addition to the parameters and frequency of measurement, the water quality program should also determine the necessary action in case of deviation.

Warning, stop and reopen limits should be written before operation. In an interactive water fountain, a sanitization failure or visible contamination should not end with just registering a warning.

Microbial testing is not a substitute for daily monitoring; The test result is specific to the sample and time.

In the event of fecal contamination, the entry of an unknown substance or the possibility of related disease, general use is stopped and specific instructions for the same event are implemented. A fixed "shock" program is not suitable for all incidents.

25–15. Material safety and storage design

Chemicals must be delivered with a label, safety data sheet and specified storage conditions. Responsible employees must also have training appropriate to their duties.

Main items in design and operation:

• Separating incompatible materials and preventing mixing of spills;

• Controlled ventilation and access;

• Dedicated and compatible containers and tools;

• Personal protective equipment according to the label and safety sheet;

• access to emergency facilities according to the risk assessment;

• Record repairs of pumps, hoses and injection connections.

CDC emphasizes prevention of drug mix-ups, staff training, and maintenance of injection systems. Safety of water purification chemicals - CDC ^[169]

Direct combination of chlorinated products with acid can create toxic gas. Injection paths, mixing points and protection during shut-down should be designed so that concentrated materials do not come into contact with each other. Risks of mixing and not interrupting the injection - CDC ^[170]

Figure note from the source manuscript

Figure 25-4

Suggested image: Photo of material storage and injection site showing tank separation, labels, spill collection chamber and access route. The image should be selected from the actual reviewed implementation.

Caption: "Injection safety begins with the placement and separation of materials and continues with training and maintenance."

25–16. Launch, delivery and ongoing management

Before operation, it is not enough to turn on the equipment. It must be shown that the complex provides the required water quality and operating conditions.

Delivery documents must include the following:

• Basis for designing and classifying the use of fountains;

• Results of water supply source testing;

• Volume, flow and equipment capacity calculations;

• Specifications of the filter bed and washing program;

• Performance documents and the permitted scope of the secondary disinfection unit;

• setpoints, warning limits and stop logic;

• Sampling and calibration program;

• cleaning procedure, long stop and restart;

• Pollution response guidelines and reopening conditions;

• Training records and responsibility of people.

Commissioning testing should also cover the logic of stopping injection in the absence of flow, the response to secondary disinfection failure, and the accuracy of alarms. These tests are carried out under controlled conditions and before public use.

In the operating budget, the cost of materials, washing water, lamps and consumables, testing, trained staff and cleaning should be considered. Buying equipment without providing these resources does not guarantee sustainable water quality.

In chapter 26: electrical installations, fountain electrical protection and safety, power supply design, panels, cabling, wet environment protection, ground connection and bonding, equipment coordination and pre-operational tests will be reviewed.