Ferrari, F., Zahedi, S., Rodríguez-Roda, I., Pijuan, M.
ICRA Catalan Institute for Water Research, H2O Building, Scientific and Technological Park of the University of Girona, 101 carrer Emili Grahit, 17003 Girona, Spain
Keywords:ambient temperature; AnMBR; biomethane; BMP; domestic wastewater.
Introduction
Anaerobic membrane reactor (AnMBR) technology has been postulated as a good strategy for treating medium-high strength wastewaters (WWs) keeping high chemical oxygen demand (COD) removal efficiencies and good methane production even at very low HRTs. However, the start-up of these reactors, especially when dealing with domestic wastewater with relatively low temperatures and low COD concentrations, have been proved to be long. The aim of this study was to assess the effect that different temperatures, wastewater concentrations and inoculum-substrate (I/S) ratios have on the methane production potential of an anaerobic sludge. This work is conducted within the scope of a project that aims at obtaining reused water from sewer mining via a forward osmosis process and energy in the form of methane from the anaerobic treatment of the concentrate produced in the FO process.
This information will be very useful for the start-up of an AnMBR treating the concentrate solution produced during the forward osmosis (FO) process.
Material and methods
Two different sets of experiments were conducted. The first one aimed at evaluating the efficiency of anaerobic digestion (AD) of WW at 3 different temperatures (37 ºC , 23ºC and 15 ºC) using the same I/S ratio (2.0) and 3 substrate COD concentration, representing 8, 4 and 2 times the COD concentration factors of a FO process treating medium strength WW with a 90%, 80% and 45% water recovery respectively (Ansari et al., 2015). In the second set of tests the effect of different I/S ratio (1.0, 1.5, 2.0 and 2.5) during the WW anaerobic degradation was evaluated.Tests were performed in 250 mL serum bottles. Inoculum was taken from a mesophilic anaerobic digester operating at 37 ºC and treating a mixture of primary and waste activated sludge from a local wastewater treatment plant. The average inoculum composition was 15.08 g COD/L, 13.7 g ST/L (58%VS) and pH was equal to 7.42.
Experimental conditions are shown in Table 1. To reach target substrate COD concentrations, a synthetic FO concentrate solution (SYNTHES) (Aiyuk & Verstraete, 2004) was used as substrate. For each I/S ratio and temperature, 2 blanks were prepared to verify the residual biogas production of the inoculum. Bottles were flushed with 100% N2 gas for 1 min, sealed with a rubber stopper retained with a plastic top and stored on an orbital shaker that was placed in a temperature controlled incubator. Biogas production was determined with the pressure transducer technique and the percentage of methane in the biogas with a gas detector (GIR-3000, GasTech). The maximum specific methanogenic activity (SMA) was calculated dividing the CH4 produced in grams of COD (considering the theoretical conversion of 0.35L CH4/gram COD) with the product of the volatile solids (VS) present in the inoculum and the
The IWA S2Small2017 Conference on Small Water & Wastewater Systems and Resources Oriented Sanitation
days of the interval of time considered. The specific methanogenic production was calculated by dividing the cumulated CH4 produced (mL CH4) with the COD initially present in the substrate. Dissolved CH4 was determined at the end of the experiment through gas chromatography.
Results and discussion
The main results obtained are shown in Table 1 and Figure 1. The first set of experiments (Set 1) showed that lower temperatures lead to lower methane yield, lower maximum methanogenic activity and higher lag phases; same I/S ratio and substrate with lower COD concentrations led to lower COD conversion to CH4 and lower maximum SMA. Results from Set 2 showed that decreasing the I/S ratio fosters the biometanization of WW, indeed lowering the I/S from 2 to 1, implied an increase in the SMA and COD conversion to CH4 of 90% and 40% respectively.
Table 1. Experimental conditions applied in each experiment and main results obtained
Set 1 Set 2
Substrate COD (gCOD/L) 3.44 3.44 3.44 1.72 1.72 1.72 0.86 0.86 0.86 3.77 2.51 1.89 1.51
I/S ratio 2.0 2.0 2.0 2.0 2.0 2.0 2.0 2.0 2.0 1.0 1.5 2.0 2.5
x Increasing temperatures accelerate WW biodegradation and shorten the period of max SMA.
x Increasing organic loads keeping the I/S ratio constant implies an increase in the biomethane production and methanogenic activity.
x Increasing organic loads lead to increasing WW biomethanization.
References
Aiyuk, S., & Verstraete, W. (2004). Sedimentological evolution in an UASB treating SYNTHES, a new representative synthetic sewage, at low loading rates. Bioresource Technology,93(3), 269–278.
Ansari, A. J., Hai, F. I., Guo, W., Ngo, H. H., Price, W. E., & Nghiem, L. D. (2015). Selection of forward osmosis draw solutes for subsequent integration with anaerobic treatment to facilitate resource recovery from wastewater. Bioresource Technology,191, 30–36.
Parallel session 1 - Greywater Treatment 08:10-09:30 Session chair: Makarand M. Ghangrekar
440 - Electrocoagulation of domestic and office-building greywater FRIEDLER Eran - Faculty of Civ. & Env. Eng., Technion - Israel Inst. of Technology
448 - Impact of suspended solids and organic matter on chlorine disinfection efficiency of greywater FRIEDLER Eran - Faculty of Civ. & Env. Eng., Technion - Israel Inst. of Technology
449 - Long term micropollutant removal in a Vertical Ecosystem for decentralised greywater reuse in a Euro-Mediterranean resort
KISSER Johannes - Alchemia-Nova
434 - The alternative use of Pseudomonas aeruginosa as an indicator on the disinfection of greywater PAULO Paula - Federal University of Mato Grosso do Sul - UFMS
Parallel session 2 - Infiltration systems 09:50-11:10
Session chair: Srikanth Mutnuri
497 - Greenhouse gas emissions from soil treatment units of on-site domestic wastewater treatment sys-tems in Ireland
SOMLAI-HAASE Celia - Trinity College Dublin
299 - The performance of a self-contained recirculating evapotranspiration system in tropical and temper-ate climtemper-ates
KELE Ben - Central Queensland University and Arris Pty Ltd
483 - Willow evapotranspiration systems to mitigate surface water pollution from domestic wastewater in rural areas with low permeability soils
GILL Laurence - Trinity College Dublin
259 - Effects of nitrogen and organic shock loadings on a soil filter treating matured landfill leachate GUAN Yidong - Nanjing University of Information Science and Technology
Parallel session 3 - Treatment wetlands 1 11:30-12:50
Session chair: Carlos Arias
524 - Combination of constructed wetlands and photocatalysis processes for the elimination of persistent organic pollutants from municipal wastewater
GONZALO Gael - University of A Coruña
566 - Constructed wetlands planted with willow for domestic wastewater treatment under cold climate GREBENSHCHYKOVA Zhanna - IMT Atlantique
274 - Efficiency of a short rotation willow coppice for the treatment of municipal wastewater under a North American humid continental climate
LACHAPELLE T. Xavier - Polytechnique Montréal
514 - Domestic wastewater treatment by a two stage vertical subsurface flow constructed wetland: removal efficiency
SEGURA Irleth - Mexican Institute of Water Technology
Tuesday 24 October
Salle G
The IWA S2Small2017 Conference on Small Water & Wastewater Systems and Resources Oriented Sanitation