CONTRIBUTION OF INERT WASTE IN DETERIORATING URBAN AMBIENT AIR QUALITY

Abstract

Developing countries are exhaustively involved in construction activities as visible from their budgets and ground realities. This involves all sorts of earth material resources from soil, rocks to cables and aluminum channels for building a structure. During such activities, a large amount of construction material is wasted. This waste not only creates hindrance in solid waste management, but gives ugly look and chokes open drains, while particulate matter (PM) is also generated which causes life-threatening health effects. Therefore, waste and PM are imperative to be monitored in any country in order to improve air quality of its cities. Generally monitoring of suspended particulate matter (SPM) needs sophisticated and costly equipment, highly trained manpower and expensive resources including continuous supply of energy, which the countries like Pakistan lacks. In order to overcome such issues, a study aiming at simple, less expensive and cost effective method to assess the amount of construction waste material generated and resulting SPM based on physio-chemical analysis of waste material was conducted. This has been achieved by the estimation of physico-chemical characteristics of SPM only by determining the same characteristics of fine inert material and the prediction of SPM, PM10 and PM2.5 concentration away from the source of construction waste generation. In order to carry on, a structured questionnaire was distributed among 800 stakeholders, including civil engineers, architects, quantity surveyors and contractors from large, medium and small cities namely: Lahore, Gujranwala, Sialkot, Gujrat and Kharian, were approached for the assessment of construction waste. For monitoring physico-chemical analysis of left over waste material and its contribution in local air quality from four construction projects/sites in Lahore, Gujrat, Kharian and Rawalpindi/Islamabad (construction of Metero Bus mega project) was investigated during various seasons (2013 – 2015) and at different construction stages of the project. In order to accomplish the objectives, a total of 168 samples including 84 samples of fine inert material and similar number of samples of corresponding SPM, were collected from the selected construction site in Lahore whereas, a total of 1764 samples, 147 of each SPM, PM10 and PM2.5 at 3, 8, 13 and 18m distance from the source of generation at other three construction sites. Analysis included pH, electrical conductivity trace metals (Al, Ca, Ni, Fe & Zn) and ions (SO4-2, NO3- & Cl-) of fine inert material and corresponding PM which were used in developing regression-based statistical models to estimate physico-chemical characteristics of SPM. The study concluded that construction materials wastage accounted for an average of 9.88% due to poor transportation, error in calculations/cutting, improper storage, over ordering and poor material handling. The PM concentration was observed well beyond the permissible limits (NEQS) at all construction sites, except the sites where recommended measures like watering were being adopted to control the PM generation. The statistical analysis showed highly significant correlation and regression between (i) all the physico-chemical parameters of fine inert material and corresponding PM, and (ii) concentrations of SPM, PM10 and PM2.5 at 3, 8, 13 and 18m at all construction sites, and the linear regression model has been proposed and tested to estimate physico-chemical characteristics of SPM from the corresponding characteristics of fine inert material. The residual error percentage difference of less than 20% in case of estimation of physico-chemical characteristics and less than 10% in case of estimation of concentration at varying distances from source of generation signifies the reliability of proposed model.