Calculating Hypochlorite Needs for Effective Water Disinfection

If a total chlorine dosage of 6.9 mg/L is required for disinfection, and the effluent flow is 11700 m3/d with 65% available chlorine in hypochlorite, how many kg/d of hypochlorite is needed?

• A. 100 kg/d
• B. 124 kg/d
• C. 150 kg/d
• D. 180 kg/d

Answer: (B)

To determine how many kilograms per day of hypochlorite are needed for disinfection, we start by calculating the total chlorine dosage required in kilograms based on the given effluent flow and the required dosage in mg/L. First, convert the effluent flow from cubic meters per day to liters per day, since 1 m³ is equal to 1000 liters. Therefore, 11,700 m³/d is equivalent to 11,700,000 liters per day. Next, we need to calculate the total dosage of chlorine required per day. This is achieved by multiplying the flow in liters by the dosage in mg/L: Total chlorine (kg/d) = (Flow in liters per day) × (Chlorine dosage in mg/L) / 1,000,000 Using the numbers provided: Total chlorine (kg/d) = (11,700,000 L/d) × (6.9 mg/L) / 1,000,000 = 80.73 kg/d However, since the hypochlorite solution contains only 65% available chlorine, we need to determine how much hypochlorite is necessary to provide the required chlorine amount. To find the amount of hypochlor

As a student preparing for your Water Treatment Operator-in-Training (OIT) exam, understanding how to calculate the amount of hypochlorite needed for disinfection is crucial—and there’s nothing quite like a splash of real-world application to help you learn! So, let’s roll up our sleeves and get into the nitty-gritty of this important topic.

Why Is Disinfection Important?

First things first—why do we even bother with disinfection in water treatment? Well, safe drinking water is a cornerstone of public health. Disinfection ensures harmful pathogens are eliminated, protecting communities from disease—pretty important stuff. To achieve this, many facilities rely on chlorine or hypochlorite. But here’s the catch: you’ve got to know how much to use!

The Hypochlorite Equation Breakdown

Let’s say you’re required to achieve a total chlorine dosage of 6.9 mg/L and your effluent flow is 11,700 m³ per day. You might think, “How am I going to figure that out?” Well, hang tight, and let’s do the math together.

First, we convert the flow from cubic meters to liters. A cube filled with water is one thing, but we want to talk liters because it makes calculations simpler. Remember, 1 m³ equals 1,000 liters, so:

11,700 m³/d = 11,700,000 L/d.

Now, for the real heavy lifting—calculating the total dosage of chlorine required. Take that flow rate and multiply it by the required dosage:

Total chlorine (kg/d) = (Flow in liters per day) × (Chlorine dosage in mg/L) / 1,000,000.

Plugging in our numbers, we get:

Total chlorine (kg/d) = (11,700,000 L/d) × (6.9 mg/L) / 1,000,000 = 80.73 kg/d.

Great! We have a figure, but hold on; not so fast, because we still need to determine how much hypochlorite is needed to achieve this dosage.

Calculating Hypochlorite Needs

Now comes the twist in our tale—hypochlorite solutions only contain a certain percentage of available chlorine. In our case, it’s 65%. So, we have to adjust our figures to find out how much hypochlorite is required to yield that 80.73 kg/d of chlorine.

To find the hypochlorite dosage that will give you that required chlorine, you’ll use the formula:

Hypochlorite Requirement (kg/d) = Total chlorine required (kg/d) / Percentage of available chlorine.

Plugging in our details:

Hypochlorite Requirement = 80.73 kg/d / 0.65 = 124.07 kg/d.

Rounding this, you would need approximately 124 kg/d of hypochlorite to properly disinfect the water.

Bringing It All Together

So, next time you’re faced with a similar question on your exam or in the field, remember, it’s all about understanding the relationships between flow rates, dosage, and the reality of chemical concentrations. Never underestimate the practical application of what you’re learning. After all, that knowledge not only helps you see the bigger picture, but it also boosts your confidence as a future Water Treatment Operator.

If you think about it, calculations like this can seem overwhelming at first. Yet, breaking it down step-by-step—just like we did—can make a world of difference. Just think, understanding this not only prepares you for your upcoming test but also for a vital role in keeping your community safe. How's that for tying it all back together?

Before you know it, you’ll be solving problems like these in your sleep. Happy studying!