Биофильтр уже работает.

Because биофильтр is singular: it means biofilter, not biofilters.

The verb работает is the 3rd person singular form of работать (to work / to operate).

• биофильтр работает = the biofilter works / is working
• биофильтры работают = the biofilters work / are working

So the verb form matches the singular subject.

It is in the nominative singular, because it is the subject of the sentence — the thing doing the action.

You can think of the basic structure as:

• Биофильтр = subject
• уже = adverb
• работает = verb

So this is a very straightforward subject + adverb + verb sentence.

Yes. Биофильтр is a masculine noun.

A common rule in Russian is:

• nouns ending in a consonant are usually masculine
• nouns ending in -а / -я are often feminine
• nouns ending in -о / -е are often neuter

Since биофильтр ends in the consonant -р, it is masculine.

In this sentence, that does not visibly change the present-tense verb form, but it would matter in other contexts, especially in the past tense:

• Биофильтр работал = The biofilter was working / worked

Уже usually means already.

In this sentence, it tells you that the biofilter is functioning now, and that this may be earlier than expected, by this point, or no longer not working.

So:

• Биофильтр работает = The biofilter is working
• Биофильтр уже работает = The biofilter is already working

The word уже often adds a sense of progress, readiness, or change of state.

That is the most natural neutral position here.

Russian word order is more flexible than English, but different orders can shift the emphasis.

Neutral version:

• Биофильтр уже работает.

Other possible orders:

• Уже работает биофильтр. = more emphasis on already working
• Биофильтр работает уже. = possible in context, but less neutral and more marked

So the given order is the most standard way to say it.

It can mean both, depending on context.

Russian present tense does not make the same strict distinction that English does between:

• works
• is working

So Биофильтр работает can mean:

• The biofilter works
• The biofilter is working
• The biofilter is operating

Context tells you which English translation sounds best.

With уже, English often prefers:

• The biofilter is already working or
• The biofilter is already operating

Yes, absolutely.

In Russian, работать is very commonly used not only for people but also for:

• machines
• devices
• systems
• programs
• equipment

So биофильтр работает sounds perfectly natural and means that the biofilter is functioning or operating properly.

Russian has no articles.

English distinguishes between:

• a biofilter
• the biofilter

Russian does not use separate words like a or the. Whether биофильтр means a biofilter or the biofilter depends on context.

So Биофильтр уже работает could mean:

• The biofilter is already working
• A biofilter is already working

In most real contexts, the situation makes it clear which one is meant.

The stress is:

• биофи́льтр
• уже́
• рабо́тает

A rough pronunciation guide:

• биофи́льтр ≈ bee-ah-FEEL-tr
• уже́ ≈ oo-ZHE
• рабо́тает ≈ ra-BO-ta-yet

A rough full pronunciation: bee-ah-FEEL-tr oo-ZHE ra-BO-ta-yet

A few notes:

• ж sounds like the s in measure
• unstressed о is often pronounced closer to a
• ь in фильтр is a soft sign; it softens the preceding consonant

It can suggest that idea, but it does not explicitly say started.

Биофильтр уже работает simply states the current result: the biofilter is already in operation.

If you want to say has already started working more explicitly, Russian would often say:

• Биофильтр уже начал работать.

That means:

• The biofilter has already started working
• literally, The biofilter already began to work

So the original sentence focuses on the current state, not the beginning itself.

It is a completely natural, full sentence.

Russian often uses short sentences like this, especially in technical, operational, or status-report contexts.

For example, it could appear in:

• a system update
• a maintenance report
• a technician’s message
• a product description
• a control panel status explanation

So Биофильтр уже работает. sounds concise, normal, and idiomatic.