The last few years have witnessed an increase in energy consumption in Information and Communication Technology (ICT). Naturally, energy efficient solutions are becoming crucial for both local and wireless access networks. In this paper, we propose a new framework to support energy efficient management in Wireless Mesh Networks (WMNs). A key distinguishing feature of our solution is its online flow-based routing approach since existing flows are dynamically consolidated or even re-routed at fixed intervals according to live arrival and departure of mesh clients. The proposed solution is compliant with emerging Software Defined Networking (SDN) paradigm since it relies on a central controller to monitor and manage the network. To achieve this, we first formulate the problem as an integer linear program (ILP). As this problem is known to be NP-hard, we then propose a simple yet efficient Ant Colony-based approach to solve the formulated ILP problem. Through extensive simulations, we show that our proposed approach is able to achieve significant gains in terms of energy consumption, compared to conventional routing solutions such as the Shortest Path (SP) routing, the Minimum link Residual Capacity routing metric (MRC) and the load balancing (LB) scheme. Specifically, we show that our approach reduces the energy consumption by up to 13%, 20%, and 52%, compared to MRC, SP and LB, respectively, while achieving the required QoS.