Impact of sewage discharges on coastal water quality of Mumbai, India: present and future scenarios Ritesh Vijay & Trupti Mardikar & Rakesh Kumar Received: 23 November 2015 /Accepted: 12 June 2016 # Springer International Publishing Switzerland 2016 Abstract The simulation study assesses the impact of sewage discharges on the present and predicted water quality of the Mumbai coast using MIKE 21. Water quality parameters in terms of dissolved oxygen (DO), biochemical oxygen demand (BOD) and faecal coliform (FC) are checked against specified standards. The simu- lation is validated for the present coastal hydrodynamics and observed water quality parameters. The validated model is further used for predicting scenarios in terms of upgradation in a pumping station and improvement in wastewater collection, treatment level and disposal sys- tems. The water quality of the existing coastal environ- ment does not conform to the stipulated standards but improves considerably in the prediction scenarios. How- ever, despite a marked improvement in FC, it is not as per desired standards as no treatment for bacteria remov- al is considered. The simulation study emphasizes the need for exploring options like the reuse or recycle of treated effluent, as an effort for water conservation. Keywords Coast . Hydrodynamics . Outfall . Sewage . Water quality Introduction Mumbai city is situated on the west coast of India and was earlier an archipelago of seven islands, now standing on reclaimed land. It is indented with the Mithi River and three major creeks, viz. Manori, Malad and Mahim on the west. Out of these, Mahim and Malad Creeks are heavily polluted (Sardar et al. 2010; Vijay et al. 2011a). Presently, the west coast receives untreated wastewater/sewage from drains and treated effluent from preliminary (Malad), primary (Worli and Bandra) and secondary (Versova) levels of wastewater treatment facilities (WWTFs) (Vijay et al. 2011b, 2015). These discharges deteriorate the qual- ity of coastal water though it has huge dilution and assim- ilation capacity (Liu et al. 2007; Kamble and Vijay 2011; Vishnuradhan et al. 2014). Sewage contains organic mat- ter and faecal coliform (FC) which experiences bacterial decomposition that reduces dissolved oxygen (DO) and increases biochemical oxygen demand (BOD) in the wa- ter. Discharges of sewage and wastewater in the coastal environment become a serious concern and challenge to the water authorities that require proper planning and management (Islam and Tanaka 2004; Jones et al. 2011; Cahoon et al. 2016). Water quality management requires the monitoring and modelling of coastal water to understand and to predict the behaviour of a coastal system due to the consequences of sewage and wastewater discharges (Esen et al. 2012; Menendez et al. 2013; Islam et al. 2014; Vijay et al. 2014; Mishra et al. 2015). Water quality models play a critical role in the evaluation of management alternatives prior to project implementation (Kuo et al. 2005; Ji 2008; Environ Monit Assess (2016) 188:420 DOI 10.1007/s10661-016-5418-9 R. Vijay (*) : T. Mardikar : R. Kumar Environmental Systems Design and Modelling Division, CSIR-National Environmental Engineering Research Institute, Nehru Marg, Nagpur 440020 Maharashtra, India e-mail: r_vijay@neeri.res.in