www.sciencejournal.in Volume- 4 Issue- 2 (2015) ISSN: 2319–4731 (p); 2319–5037 (e) © 2015 DAMA International. All rights reserved. 249 ESTIMATION OF THE FUNCTION OF RETENTION TIME RESPONSE FROM COMMON ANAEROBIC DIGESTION OF URBAN BIOMASS RESOURCES IN VITRO Mehdi Mashayekhi-Rad 1 , Morteza Almassi 2 *, and Saeed Minayee 3 1, 2, 3 Department of agricultural mechanization, Science & Research Branch, Islamic Azad University, Tehran, Iran 1Email: m.mashayekhi.r@gmail.com 2Email: Morteza.almassi@gmail.com 3Email: sminaee@gmail.com *corresponding author: Morteza Almassi ABSTRACT One of the most important ways to manage the urban biomass is biological digestion of conversion of organic material which the main product of that is methane. Regarding to the daily production of waste and their cumulative increase, the item of time and its management for consumption and common digestion of these sources is very important. Thus in this article, the response function of retention time of co-digestion from multi-source biomass (Wet waste, excreta consisting of a mixture cattle and poultry excreta (50% each) and industrial waste a mix of cattle slaughterhouse waste, poultry slaughterhouses, plant oils and fish cannery each one 25%) were estimated. The effect of environmental factor of temperature and nature factor of C / N ratio was determined as the time of composition of sources was evaluated. To estimate the function, the “Combined Mixture -Process design” was used by the “Design-Expert” software. Based on results, the interaction of three sources with the impact factor of -113.05 had the maximum effect and the negative sign shows the opposite effect (decrease) over the time. After that the main effects of industrial waste, excreta, and wet waste had positive coefficients of 24.01, 20.79 and 20.00, respectively and then the interactions of excreta and industrial waste, wet waste and industrial waste, excreta and wet waste had the coefficients of 6.40, 4.04 and 2.36, respectively. Any process order of design was not significant for evaluation of the effect of temperature and the ratio C / N. So in the estimation function these two factors were not included. KEY WORDS: response function, retention time, co-digestion INTRODUCTION Millions of tons of organic waste annually are produced in urban and rural areas and the proper management of landfill and disinfecting of them are the main concerns of the communities today. Nowadays the production of energy is used as a preferred option in the management of urban waste and the amount of produced energy by waste is growing considerably each year. One method of energy production is anaerobic digestion of organic materials that methane is its main product. The other important aspects of renewable energy (making healthy environment, rich fertilizer production and use of cheap raw materials) also have their own importance. Due to the variety of waste and the daily mass production of each of them and the importance of time in digesting, the urban managers seek common anaerobic digestion at the appropriate time to improve their management systems. Therefore, estimating the response time for the anaerobic digestion of these resources can help to make it. Comparison of methane production from different resources and the influential factors are labor-intensive and time-consuming when done only by laboratory experimentation because of the multiplicity of experiments. It is beneficial to develop a method or model that compares resources using specific and limited experimental data to consider influential conditions. Combined mixture-process design is a statistical technique which combines mixture components (That add to a fixed total. For instance, A is 10% of the mixture, B is 30%, and C is the remaining 60%. If the percentage of one component is increased, then the percentage of one or more of the other components must be decreased) and process factors. It can involve blending ingredients in an oven and determining how they interact using one or several factors, such as temperature and C/N ratio. The main advantage of this plan is a reduction in the number of experiments required to evaluate the multiple parameters and their interactive relations. Literature Review Anaerobic digestion mechanism In the first stage, complex organic materials such as carbohydrates, fats, and proteins are converted into simple organic materials such as simple sugars, fatty acids, and amino acids using acidogen bacteria. These change compound organic