Many travelers takes it a given that every lodge shall be, by their very essence, green in such a place as Tanzania. But it would be a way to forget that sustainability is not to be reduced to buying local and saving energy; it englobes a lot more of criteria and goals.
Because many travel companies, as well as local actors, see Eco-tourism as a pure marketing strategy, forgetting about the very goal of sustainability : preservation. According to the World Tourism Organization, sustainable tourism should lead to the "management of all resources in such a way that economic, social and aesthetic needs can be fulfilled while maintaining cultural integrity, essential ecological processes, biological diversity and life support systems".
Luckily, others regard it as a genuine effort to imaginatively dispose of waste, employ and train local people, preserve the environment and support local communities.
You can check for successful examples here, lodges and hotels that manage the difficult task to combine comfort and natural preservation.