I am concerned about healthy eating and the environment, t. That’s why five years ago I decided to joining a consumer cooperative for my grocery purchases. I am concerned about healthy eating and the environment. That’s why five years ago I decided to join a consumer cooperative for my grocery purchases.

In some formal writing settings it's desirable for sentences complete in themselves to be separated by a colon, semicolon or period. In other contexts a comma is fine.

I am concerned about healthy eating and the environment, that’s why five years ago I decided to joining a consumer cooperative for my grocery purchases. I am concerned about healthy eating and the environment, that’s why five years ago I decided to join a consumer cooperative for my grocery purchases.

Almost every neighborhood in my city has one of thisese groups of citizens, that work together to make a better world. Almost every neighborhood in my city has one of these groups of citizens that work together to make a better world.

'This' or 'these' agrees in number with the noun it accompanies: 'this group', 'these groups'. Either 'citizens who work together' or 'citizens that work together' is fine. I've taken out the comma because it is unusual to break up a clause in that way: [one] [of these groups] [of citizens that work together].

Almost every neighborhood in my city has one of thisese groups of citizens, thatwho work together to make a better world. Almost every neighborhood in my city has one of these groups of citizens, who work together to make a better world.

How it works? How it works?

'How it works' or 'How does it work?' might read more smoothly.

How does it works? How does it work?

Periodically I can buy fruit, vegetables and meat directly from small farmers that use ecological procedures to grow them. Periodically I can buy fruit, vegetables and meat directly from small farmers that use ecological procedures to grow them.

'Ecological procedures' is good, but 'sustainable processes' or 'ecologically friendly processes' might read as more natural.

Periodically I can buy fruit, vegetable, and meat directly from small farmers thatwho use ecological procedures to grow them. Periodically I can buy fruit, vegetable, and meat directly from small farmers who use ecological procedures to grow them.

Thatis is quiteof considerable benefit forto them because there are no brokers. This is of considerable benefit to them because there are no brokers.

This is fine, but 'quite considerable' is an expression to avoid in formal writing: 'considerable' alone communicates the degree of benefit, so 'quite' is a tautology. 'This is to their benefit' or 'this is of benefit to them'.

That is quite a considerable benefit for them because there are no brokers. That is quite a considerable benefit for them because there are no brokers.

Obviously, this system is not as cozy as going to a supermarket. Obviously, this system is not as cozy as going to a supermarket.

'Cozy' reads strangely here. 'Convenient'?

Obviously, this system is not as cozy as going to a supermarket. Obviously, this system is not as cozy as going to a supermarket.

convenient or comfortable could fit here

I must clean deeply every single item. I must clean deeply every single item.

This is fine, but 'I have to carefully clean', for example, might sound more natural to a native speaker. Frustratingly, although we 'deep clean' we don't 'clean deeply'!

I must clean deeply every single item well. I must clean every single item well.

IOn the other hand, this assures me that there’s no phytosanitary product has been applied. On the other hand, this assures me that no phytosanitary product has been applied.

'On the other hand'. I've rearranged the rest of the sentence to show a construction that seems more natural to me: 'there is no product [that has been] applied' ---> 'no product has been applied'.

IOn the other hand, this assures me that there’s no phytosanitary product applied. On the other hand, this assures me that there’s no phytosanitary product applied.

HOne hundred percent natural food, without plastic containers. One hundred percent natural food, without plastic containers.

'One hundred percent' or 'a hundred percent'. You could turn this into a full sentence to make the composition as a whole read more smoothly.

HIt's a hundred percent natural food without plastic containers. It's a hundred percent natural food without plastic containers.

You could connect this with the previous sentence

I know that this will not improve the alarming statuse of the planet, but I try to do mymake a small contribution. I know that this will not improve the alarming state of the planet, but I try to make a small contribution.

I know that this will not drastically improve the alarming status of the planet, but I try to do my small contributioncontribute in my own small way. I know that this will not drastically improve the alarming status of the planet, but I try to contribute in my own small way.