Identify the correct statements regarding the activated sludge process:

1. It involves the aeration of wastewater to promote the growth of microorganisms.

2. The process results in the formation of biological sludge, which is partially recycled.

3. Protozoa, such as Amoebae and Peritrichs, indicate an unhealthy condition of the sludge.

4. The process is anaerobic and does not require oxygen.