Elektroodpady nie są w tym pojemniku.

Because elektroodpady is grammatically plural in Polish.

• jest = is (singular)
• są = are (plural)

So:

• Elektroodpad jest... = The electrical waste item is... / E-waste is... if treated as singular
• Elektroodpady są... = E-waste items are...

In this sentence, elektroodpady means multiple items of electrical waste, so są is correct.

Elektroodpady means electrical waste, electronic waste, or e-waste.

It is made from:

• elektro- = relating to electricity/electrical things
• odpady = waste, rubbish, refuse (plural)

In everyday Polish, this usually refers to old or broken electrical/electronic devices that need special disposal.

Nie is the normal Polish word for not.

So:

• są = are
• nie są = are not

Polish forms standard negation by putting nie before the verb:

• jest → nie jest
• są → nie są
• mam → nie mam

So Elektroodpady nie są... simply means E-waste is not / E-waste items are not...

After w meaning in, Polish normally uses the locative case.

That is why:

• ten pojemnik = this container (nominative)
• w tym pojemniku = in this container (locative)

Both words change:

• ten → tym
• pojemnik → pojemniku

So w tym pojemniku literally means in this container.

Because Polish demonstratives like ten (this) must agree with the noun in gender, number, and case.

Here, pojemnik is:

• masculine
• singular
• in the locative case after w

So the correct form is tym.

A few related forms:

• ten pojemnik = this container
• tego pojemnika = of this container
• temu pojemnikowi = to this container
• w tym pojemniku = in this container

Because it is in the locative case, triggered by w in the sense of in.

The base form is:

• pojemnik = container/bin

In the locative singular, many masculine nouns take -u or -e, so here:

• pojemnik → pojemniku

This is something you usually have to learn with noun patterns over time.

Yes. That would mean:

• Elektroodpady nie są w pojemniku = The e-waste is not in the container / not in a container

Adding tym makes it more specific:

• w tym pojemniku = in this container

So tym is like pointing to a particular one.

Yes, that is a very useful thing to notice.

English often uses e-waste like a mass/uncountable noun, but Polish commonly uses elektroodpady, which is a plural noun. So even if the English translation looks singular-ish, the Polish grammar is plural:

• Elektroodpady są...
• not Elektroodpady jest...

This kind of mismatch between English and Polish is common.

Yes, Polish word order is more flexible than English, although the original sentence is the most neutral.

Neutral version:

• Elektroodpady nie są w tym pojemniku.

You might also hear:

• W tym pojemniku nie ma elektroodpadów.
• Nie ma elektroodpadów w tym pojemniku.

These versions are also natural, though they are built differently. The sentence with nie są focuses on electro-waste not being in this container, while nie ma is another very common way to say there is/are not.

Polish has no articles like English a/an/the.

So:

• pojemnik can mean a container or the container
• elektroodpady can mean electrical waste, the electrical waste, or e-waste items

Specificity is usually understood from context, or shown with words like:

• ten = this
• tamten = that
• jakiś = some

Here, tym pojemniku helps specify this container.

Roughly: eh-lek-tro-ot-PA-dih

A few tips:

• Stress in Polish is usually on the second-to-last syllable
• So here the stress is on pa: elektroodPAdy
• dy at the end sounds roughly like dih, not like English die

Also notice that oo here is not a special long vowel; it is just the end of elektro- plus the beginning of odpady coming together in one word.

It can mean container, bin, or receptacle, depending on context.

In signs and public instructions, pojemnik often means a waste bin/container. So in this sentence, it probably refers to a specific bin for rubbish or recycling.

Yes, it sounds natural, especially in written instructions or signage.

It has the tone of:

• E-waste does not go in this container
• No e-waste in this bin

If the goal is a direct rule or prohibition, Polish signs might also use other styles, for example:

• Nie wrzucać elektroodpadów do tego pojemnika. = Do not throw e-waste into this container.
• To nie jest pojemnik na elektroodpady. = This is not a container for e-waste.

But your sentence is perfectly normal and clear.