The primary factor affecting the performance of anaerobic wastewater treatment systems is:a.pHb.Salinityc.Temperatured.Oxygen concentration

The primary factor affecting the performance of anaerobic wastewater treatment systems is temperature. Here's why:

1. Anaerobic bacteria, which are the main agents in anaerobic wastewater treatment systems, are sensitive to temperature. Their activity increases with temperature, up to a certain point.

2. The optimal temperature for most anaerobic bacteria is between 30°C and 40°C. Below this range, their activity decreases, slowing down the treatment process. Above this range, they may become inactive or die.

3. Temperature also affects the solubility and diffusion of substances in the wastewater. For example, at lower temperatures, fatty acids are less soluble and diffuse more slowly, which can inhibit the bacteria's activity.

4. Finally, temperature can influence the equilibrium of chemical reactions in the treatment process, which can affect the efficiency of the system.

Therefore, while pH, salinity, and oxygen concentration can also affect the performance of anaerobic wastewater treatment systems, temperature is generally considered the primary factor.