What are the basic RAW WATER TREATMENT challenges and how can they be avoided ?
There can be several challenges that can surface during raw water treatment when industrial companies start treating a raw water source for the different processes. Irrespective of designing a new plant or upgrading existing equipment, overcoming the five raw water treatment challenges will facilitate more efficient process operation.
The five basic challenges with raw water treatment and steps to avoid them are enumerated below.
1. Turbidity Variation
Turbidity is defined as the cloudiness of water due to the presence of a large number of particles. Due to the variation in turbidity there can be negative effects on the quality of the process and effluent from the plant.
A consistent set of years’ worth of data is definitely required to evaluate the turbidity levels coming into the plant across different seasons prior to designing of the system. If the plant is designed around the seasonal turbidity flow without taking into consideration any of the changes in turbidity, problems can surface. If the turbidity is too high, then the plant may not remove it efficiently.
This turbidity gets split over to production and can be present in the effluent discharge resulting in contamination of the process and thus the stipulated local discharge regulations cannot be met. Another challenge of varying turbidity levels is the quantity of sludge that’s generated as a result of treating the turbidity.
Normally, secondary sludge systems may not be able to handle the overload, resulting in the backing up of the sludge in the clarifier leading to the shut-down of the pretreatment system. The best way to overcome this challenge is to design a slightly oversized treatment system for turbidity, keeping in mind the turbidity variations. Additionally, it’s advisable to design a recycle system in the case of the water not meeting the quality parameters as it moves through the process.
This can be recycled through and retreated once more to be effective. An alternative method will be to prepare for varying turbidity by deploying variable controls on the chemical feed systems so as to adjust the chemical feed rates. There can be an oversized sludge handling system so there is this system that can pump out the sludge in the clarifier filters, if the turbidity does fluctuate, thereby managing it.
2. Flow Variation
Normally industrial companies make educated guesses on the flow rates. If an industrial facility is not equipped to handle these flow variations, there can be upsets to the system which will carry turbidity over and resulting in the plugging of any downstream filters. It is important to understand the peak demand and thereby holding tanks can be used to buffer out the peak demands.
This will help to prepare for drastic flow variations. Ideally, one has to design the system with an excess flow buffering cum holding capacity so that the plant can be run as consistently as possible. Furthermore, the holding tanks downstream can be used to handle surges in the production needs.
An alternative method will be to prepare for varying turbidity by deploying variable controls on the chemical feed systems so as to adjust the chemical feed rates. The system can be made to balance out more easily and also increase in functionality by using the combination of variable flows on feed treatment equipment as well as storage on peak demands.
If there is no facility to automate chemicals, then one has to test more often. The plant can be run at a consistent flow rate to avoid such upsets as well as turbidity issues. Raw water treatment plants may not handle flow variations efficiently, so it’s important to design the system taking this into consideration from the start.
3. Changing of feed water chemistry
There can be seasonal variations in water Chemistry on the surface as well as waters. To handle such variations, the Industrial plants have to take care in the design of any raw water treatment systems to be large enough.
The problem of seasonal changes in raw water iron or Silica can cause problems. If the clarifiers are not designed large enough to get the proper retention times and if the feed systems are not designed large enough to handle the increased load, then there can be carryover of silica iron into the downstream equipment.
This will result in problems such as scaling as well as fouling. Furthermore, if the higher seasonal loads of iron
and silica are not precipitated out, then particulate carryover can happen to the sludge handling systems (sludge thickening and filter pressing operations), resulting in their failure.
It’s extremely critical to understand the variations of the contaminants, feed water chemistry and then design the system in line with that. An oxidation chemical, namely oxygen as well as an aluminum-based coagulant, namely alum will precipitate out the iron as well as silica. These physical chemical processes allow iron/silica to settle so that they can be removed by a clarification filtration system.
4. Awareness of regulatory quality requirements
In the case of plants that have been installed for many years, it is possible that the design of the plant was made for a certain process (designed to deliver a particular kind of effluent quality). However, we need to adapt the equipment to account for changes in regulations, to make sure we meet stringent requirements.
For instance, take the example of feeding water to a low-pressure boiler which then gets replaced by a bigger boiler that runs at a higher pressure. Depending on the new boiler’s requirements, the quality of the feed water to the boiler may be inadequate.
To ensure that the feed water is of better quality, ancillary equipment needed to be added to the system. That is why plants should always be designed with forward-thinking in mind due to respect to the anticipated future. Moreover, this will make the plant ready for expansion and quality improvement.
This will allow space in the plant for adding additional equipment which will enable handling changes in the quality requirements.
5. Secondary waste
Ignoring secondary waste (a by-product of the process) is one of the critical mistakes made in designing raw water treatment plants. Contaminants from the feed water adversely impact the volume as well as processing requirements of secondary waste.
Also, sometimes these secondary wastes need to be treated and discharged, yet many times they are discharged to a publicly owned treatment works or wastewater facility and they must meet the requirements of that facility. It’s best to understand and analyze the regulatory requirements and design the wastewater secondary treatment processes and sludge handling to meet the effluent discharge of the plant water to the municipality/environment.
The regulatory parameters need to be followed in advance to ensure that the plant will achieve the effluent goals or discharge norms.
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