The Onomy Exchange's AMM earnings are dispersed in two ways. Firstly, to pay the respective portion of AMM earnings to liquidity providers. Second, to purchase NOM and then burn the purchased NOM from the supply.
This functionality is incentivized by providing a programmatic reward to any user who executes the buy and burn function - thus decentralizing this action and creating a competitive market amongst users to execute the function to receive the reward. Onomy carries no central management of this function.