1. How many biogas systems were in operation in the U. S. in 2017?

2,200 operational biogas systems

Biogas systems turn organic material into soil amendments and gaseous fuel by using anaerobic digestion, a natural, biological process in a sealed tank. There are more than 2,200 operational biogas systems in the U.S. today with the potential for over 13,500 new systems to be built

Explanation:

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As of August 2017, AgSTAR estimates, 250 manure anaerobic digester biogas recovery systems were in operation at commercial livestock facilities in the United States. The full potential to provide renewable energy is much greater: an estimated 8,100 U.S. dairy and swine operations could support biogas recovery systems.

Explanation:

parasites can detrimentally affect their host, but also must not allow their host to die before they can complete their life cycle. some parasites have complex life cycles with many different hosts, and have had to find ways of persisting in many different environments during the change from one host to another. ectoparasites live outside the body of the host, and can more easily  disperse, but are  more exposed to predators, parasites, parasitoids. endoparasites live inside the body of the host, and are therefore protected from the outside environment. but they can be  attacked by the host's immune system. they have therefore developed  mechanisms for dispersal such as  complex life cycles.