Rác tái chế bị lẫn với rác hữu cơ.

Bị often marks something as an unwanted or negative situation happening to the subject.

So in Rác tái chế bị lẫn với rác hữu cơ, bị shows that the recyclable waste being mixed with organic waste is a bad or undesirable thing.

It is similar to saying:

• The recyclable waste got mixed with the organic waste
• The recyclable waste was accidentally mixed with the organic waste

If you remove bị, the sentence becomes more neutral and less clearly negative:

• Rác tái chế lẫn với rác hữu cơ
  = Recyclable waste is mixed with organic waste / mingles with organic waste

With bị, the sentence sounds more like a problem.

Yes, it is passive-like, but Vietnamese does not always form passives in exactly the same way English does.

In this sentence:

• Rác tái chế = the thing affected
• bị = marks an adverse passive situation
• lẫn với rác hữu cơ = gets mixed with organic waste

So the structure is roughly:

subject + bị + verb/description

A natural English equivalent is:

• Recyclable waste is mixed with organic waste
• Recyclable waste gets mixed in with organic waste

Vietnamese often uses bị for passive situations with a negative result, while được is often used for positive ones.

Lẫn với means to be mixed with, to get mixed in with, or to be mixed up with.

It often suggests that things that should be separate are together, often unintentionally.

In this sentence:

• rác tái chế bị lẫn với rác hữu cơ = recyclable waste gets mixed in with organic waste

This is slightly different from trộn với:

• trộn với often means to mix together, sometimes more deliberately
• lẫn với often suggests being mixed among something else, often by mistake

So here lẫn với is very natural because recyclable waste and organic waste are supposed to be sorted separately.

Tái chế normally means to recycle as a verb. But after a noun, it can function like a modifier.

So:

• rác = trash / waste
• rác tái chế = recyclable waste / waste for recycling

This is a very common Vietnamese pattern: a word that is usually a verb can come after a noun and describe it.

Other similar examples:

• nước uống = drinking water
• máy giặt = washing machine
• xe đạp = bicycle

So rác tái chế literally feels like waste [for] recycling.

In Vietnamese, modifiers usually come after the noun they describe.

So:

• rác hữu cơ = organic waste
• rác tái chế = recyclable waste

This is a basic word-order difference from English, where adjectives usually come before the noun:

• organic waste
• recyclable waste

In Vietnamese, it is typically:

• noun + adjective/descriptor

That is why:

• rác hữu cơ is correct
• hữu cơ rác sounds wrong

It can correspond to all of those, depending on context.

Rác is a general word for trash/garbage/waste. In environmental or sorting contexts, English often translates it as waste, because that sounds more natural in phrases like:

• recyclable waste
• organic waste

But in everyday speech, rác can also simply mean:

• trash
• garbage

So in this sentence, waste is probably the best translation.

Vietnamese does not use articles like a, an, and the in the same way English does, and nouns usually do not change form for plural.

So:

• rác tái chế could mean recyclable waste, the recyclable waste, or even recyclables, depending on context
• rác hữu cơ could mean organic waste or the organic waste

The sentence does not explicitly mark singular or plural either. Context tells you what is meant.

That is why one Vietnamese sentence can be translated into English in several natural ways:

• Recyclable waste is mixed with organic waste
• The recyclable waste got mixed with the organic waste
• Recyclables were mixed in with organic waste

There is no explicit tense marker here.

Vietnamese often leaves tense unstated unless it is important. Time is usually understood from context or added with time words such as:

• đã = past
• đang = ongoing
• sẽ = future

So this sentence by itself can mean different things depending on context:

• Recyclable waste is mixed with organic waste
• Recyclable waste got mixed with organic waste
• Recyclable waste has been mixed with organic waste

If you wanted to make it clearly past, you could say:

• Rác tái chế đã bị lẫn với rác hữu cơ.

Usually, lẫn in this meaning is very naturally followed by với when you say what something is mixed with.

So:

• Rác tái chế bị lẫn với rác hữu cơ = natural

If you remove với, the sentence sounds incomplete or unnatural in this context:

• Rác tái chế bị lẫn rác hữu cơ = not the best standard phrasing here

Think of lẫn với as a set expression meaning mixed with.

Yes. The current sentence focuses on the recyclable waste as the affected thing. An active version would focus more on the action or on the person doing it.

For example:

• Người ta lẫn rác tái chế với rác hữu cơ.
  = People mixed recyclable waste with organic waste.

• Ai đó đã trộn rác tái chế với rác hữu cơ.
  = Someone mixed recyclable waste with organic waste.

However, the original sentence is often more natural if the speaker wants to emphasize the problem itself rather than who caused it.

Both can be translated as be mixed with, but the nuance is a little different.

• bị lẫn với: suggests being mixed in, mingled, or confused together, often unintentionally
• bị trộn với: suggests being physically mixed together, often more directly or deliberately

In waste-sorting contexts:

• bị lẫn với is very natural because it suggests one category ended up among another category
• bị trộn với is also possible, but can sound a bit more like the materials were actively stirred or combined

So the original sentence sounds appropriate for accidental contamination in sorting.

A native speaker would likely understand it as:

The recyclables have been mixed in with the organic waste, which is a problem.

The key ideas are:

• rác tái chế and rác hữu cơ are two categories that should be separate
• bị signals that this is undesirable
• lẫn với suggests accidental or improper mixing

So the sentence is not just describing physical mixture; it also implies incorrect sorting or contamination.