The domestic sewage in large cities(a) Has a high BOD as it contains both aerobic and bacteria(b) Is processed by aerobic and then anaerobic bacteria in the secondary treatment in Sewage Treatment Plants (STPs).(c) When treated in STPs does not really require the creation step as the sewage contains adequate oxygen.(d) Has very high amounts of suspended solids and dissolved salts

Out of the statements you provided, (d) "Has very high amounts of suspended solids and dissolved salts" is generally true for domestic sewage in large cities. However, the other statements are not entirely accurate. Let's go through each statement and provide more accurate information:

(a) Domestic sewage in large cities can have a high Biological Oxygen Demand (BOD) because it contains organic matter that requires oxygen for decomposition. However, it does not necessarily mean that it contains both aerobic and anaerobic bacteria. Domestic sewage usually contains a mix of aerobic, facultative, and anaerobic bacteria.

(b) In Sewage Treatment Plants (STPs), the secondary treatment typically involves a biological process where aerobic bacteria are primarily utilized to break down organic matter in the sewage. This process is known as the activated sludge process. Anaerobic bacteria are often employed in separate stages of the treatment process, such as in anaerobic digestion, to further treat the sludge generated during sewage treatment.

(c) The statement that sewage treated in STPs does not require the aeration step because it already contains adequate oxygen is incorrect. Aeration is an essential part of the treatment process in STPs. During the secondary treatment, oxygen is provided through aeration to support the growth of aerobic bacteria, which help in the decomposition of organic matter. Aeration also helps in maintaining an aerobic environment throughout the treatment process.

(d) As mentioned earlier, domestic sewage can indeed have high amounts of suspended solids, which include organic matter, debris, and other solid particles. However, the presence of dissolved salts in sewage depends on various factors, including the source of the water supply, the geographical location, and the sewerage system. While some dissolved salts may be present in sewage, their concentration can vary significantly.

It's important to note that the characteristics of domestic sewage can vary depending on various factors such as the population size, industrial activities, and local regulations. Therefore, specific details may differ for different cities and regions.