IMPROVEMENT OF SLUDGE ENERGY RECOVERY IN INTEGRATED PULP&PAPER PRODUCTION

Transcription

1 IMPROVEMENT OF SLUDGE ENERGY RECOVERY IN INTEGRATED PULP&PAPER PRODUCTION Aleksandra Račič Kozmus, M.Sc. 1), prof. dr. Andreja Žgajnar Gotvajn 2) and prof. dr. Gregor Drago Zupančič 3) 1) ZEL-EN Renewable and Sustainable Energy Development Centre, Branch Krško-Vipap, Tovarniška 18, SI-8270 Krško, Slovenia. 2) University of Ljubljana, Faculty of Chemistry and Chemical Technology, Chair of Chemical Process, Environmental and Biochemical Engineering, Večna pot 113, SI-1000 Ljubljana, Slovenia. 3) Institute for Environmental Protection and Sensors, Beloruska 7, SI-2000 Maribor, Slovenia. Green Capital of Europe 2016 City Museum, Ljubljana LJUBLJANA, 12 September 2016

2 INTRODUCTION Graphic paper mills with integrated production of recycled fiber (RCF) produced with deinking process generate large amounts of sludge kg d.m./t pap. Sludge management is economically important! Limited possibilities for sludge recovery in other sectors : cement production, ceramics and bricks production, composting. High costs for sludge treatment. Specific structure of waste activated sludge (WAS) in comparison to WAS from municipal TP. Sludge energy recovery with heat and electricity cogeneration is one of the best available techniques for sludge management (Breff PP, 2015). 2

3 RESEARCH OBJECTIVES 1. To determine the most appropriate procedure for reduction of WAS from aerobic wastewater (WW) treatment plant (TP) in investigated paper mill by a minimum of 50% Energy utilization of total sludge from paper mills with a positive energy balance. The comparison of the efficiency and economic benefits of different treatment technologies for WAS or WW. 3

4 INTRODUCTION OF INVESTIGATED RCF PAPER MILL VIPAP VIDEM KRŠKO d.d. Production: >200,000 t year -1 graphic papers (newsprint, improved newsprint). The main raw material : RCF, produced from waste paper with de-inking (up to 95% of fibers). Processing > 600 t waste paper day -1. Treatment of WW: Primary: chemicalmechanical WWTP, Secondary: aerobic BTP with activated sludge(astp) 180,000 PE. Groundwood pulp (TGW) (10% - 20%) and purchased sulphate pulp (5% - 15%). 4

5 Paper manufacture in Krško began in Extensive investments in modernising the manufacturing process were made. DIP Sludge incineration PM 1-3 BTP CMTP 5

6 PAPER MILL SLUDGES PS DIP PS CMTP WAS Sludge from DIP production. 81 m.% d.m. Net CV: 6.7 MJ kg -1 d.m. Sludge from CMTP of WW. 15 m.% d.m. Net CV: 8.2 MJ kg -1 d.m. Excess WAS from aerobic TP 4 m% d.m. Net CV: 13.7 MJ kg -1 d.m. WAS management: 40% of BTP operational cost. Energy recovery in a grate-fired incinerator with a steam cogeneration, 61,000 t year -1 of sludge, CV >3.5 MJ kg -1 d.m. ~50-60% WAS dehydration with PS CMTP The rest of WAS to external contractors 6

7 PROPERTIES OF SLUDGE FROM RCF PAPER MILLS In EU waste paper recycling rate is increasing: 71.7% (2013). A paper fiber is collected and recycled 3.5 times on average. The proportion of inorganic materials in RCF increases, RCF fibers become shorter, what worsens their dehydration properties. Increasing inorganic amount in PS (50 68 % d.m.) increasing dryness of PS (55 75%) for Caloric Value (> 3.5 MJ kg -1 ) for combustion with positive energy balance. WAS: Due to low dehydration propersties, dryness of sludge mixture of WAS with PS is reduced. 7

8 REVIEW OF THE TESTS Chemical pre-treatment of WAS and biological treatment of WAS SBR pilot test of anaerobic (AN) treatment of raw and hydrolyzed WAS Laboratory test of aerobic treatment of raw WAS and pre-treated WAS with ozone. Test of biological treatment of WW Pilot test of AN treatment on UASB reactor: WW from DIP and WW after CMTP. Pilot tests of aerobic treatment on SBR reactor : WW from CMTP outflow after AN treatment. 8

9 ANAEROBIC BIOLOGICAL TREATMENT THEORY A complex process of AN heterotrophic MO for the treatment of heavily load WW, PS or BS. The organic matter is decomposed to simple monomers, organic acids, acetate, at the end to methane. Processing takes place without the presence of oxygen, in four stages: Hydrolysis, Acidogenesis, Acetogenesis, Methanogenesis. Hydrolysis and Methanogenesis determine processing speed. 9

10 Organic compounds(c,h, O, N,P,S) CO 2 AEROBIC BIOLOGICAL TREATMENT THEORY H O 2 NO 3 PO 3 4 SO 2 4 O 2 nutrients MO H new MO E Relationship among BOD, MLVSS, oxygen utilization, and nutrients Endogenous respiration (decomposition of cell mass) C 5 H 7 O 2 N + 7O 2 5CO 2 + 3H 2 O + HNO 10 3

11 TESTS OF WAS CHEMICAL PRE-TREATMENT Alkali hydrolysis (beaker 2L, NaOH, 70 0 C, 5 h, ph=12) Ozonation (cylindrical reactor 3L, ozone generator from liquid oxygen, dosage mg O 3 g -1 VSS AB, ph= ) 11

12 CHEMICAL DEGRADABILITY OF WAS Comparison of the effects of WAS pre-treatment with hydrolysis and ozone suggests worse outcomes than those in the literature (> 50% efficiency reduction TSS). (Kaluža et al., 2014; Lee and Ye, 2007; Tsuno and Nagar, 2006) Parameter Raw WAS Hydrolyzed WAS Hydrolysis efficiency (%) Raw WAS WAS after ozonation Efficiency of ozonation (%) ph (/) / / CODf (mg O 2 L -1 ) / / TSS (g L-1) VSS (g L-1) VSS/TSS (/) VS (ml L -1 ) Note: Hydrolysis with 5M NaOH, ph=12, 4 h, 70 0 C; Ozonation with 16 mg O 3 g -1 VSS WAS. 12

13 PILOT TEST OF ANAEROBIC WAS TREATMENT Samples: raw WAS, alkali hydrolyzed WAS. SBR, T 38 0 C, OLR: kg COD m -3 R day -1, measuring the BM quantity. ph: , time: days, INFLOW/OUTFLOW OF WAS: 1 L /day. Inoculum: AN sludge from municipal WWTP, process stabilization: 12 days. Alkali trap (CO 2 and H 2 S elimination) Biomethane flowmeter biogas WAS inflow 1 INFLOW of WAS or HWAS Biogas Electric heater Biomethane Sequential batch reactor - 12 L OUTFLOW of WAS or HWAS 2 13

14 LABORATORY TEST OF AEROBIC WAS TREATMENT Samples: raw WAS, WAS after ozonation with dosage of 16 mgo 3 g -1 VSS WAS. Laboratory reactor ( L), 40 0 C, 7 10 days. The introduction of pure oxygen into the reactor to 2 8 mgo 2 L -1. On line monitoring of oxygen consumption, ph:

15 Parameter RESULTS OF WAS TREATMENT Anaerobic WAS treatment Aerobic WAS treatment Raw WAS HWAS Raw WAS WAS after ozonation Biological treatment efficiency Chemical and biolog. treatm. efficiency Biological treatment efficiency Biological treatment efficiency Chemical and biolog. treatm. efficiency Biological treatment efficiency Unite % % % % % % TSS (up to 50%) 5) (50-80%) 4) VSS (21 55) 1) (28 62) 3) COD / / / OLR / / / (kg COD m -3 R day -1 ) SMP (m 3 t -1 VSS feed ) Spec. oxygen cons. 141 (40 200) 1) 120 (11 249) 2, 3) / / / / / (go 2 g -1 VSS removed) References: 1) Meyer and Edwards (2014), 2) Bayr et al.. (2013), 3) Wood et al.. (2010), 4) Lee and Yeom (2007), 5) Eckenfelder (1980); Gaudy (1984) WAS is poorly degradable compared to the municipal WWTP sludge, it contains inhibitors for WAS degradation. This is even more evident after the WAS chemical pre-treatment. There is not known connection between the sludge biodegradation and the type of manufacturing process from the literature, results are in a wide range and are conflicting. 15.

16 Heat exchanger PILOT TEST OF ANAEROBIC WW TREATMENT Implemented in 12 L UASB reactor, T C, ph Inoculum 6L (TSS: 52 g L -1 ) of the ANA granular sludge of brewery. Q= L day -1. Process analyzed in 5 points, biogas (BG) measurement at room conditions, BG composition (14 x gas chromatography ( GC)). Process stabilization: 10x HRT (25 30 h). Testing 83 days of DIP WW and 127 days of CMTP outflow with different additives. Biogas flowmeter 5 Settler Biogas Effluent UASB reactor Gas cap / storage DIP WW Separation 0.5 mm Primary sludge 1 Total reactor volume 12 L 3 Effluent Sludge bed (biomass granules) Deflector Feed tank 120 L Influent 2 Active reactor volume 6 L Effluent tank - Clarifier 120 L Effluent sludge 4 Influent Feed pump

17 TESTED SAMPLES 1. Experiment 1: DIP WW (days 1 67), DIP WW without SS (days 68 83). 2. Experiment 2 : CMTP outflow + additives sample 1: WW CMTP outflow (days ), sample 2: WW CMTP outflow + 1 % HWAS (days ), sample 3: WW CMTP outflow + nutrients (days ). Addition of nutrients: first 12 day : 3.3 mgn L -1 & 0.8 mgp L -1, next 31 days the dose was doubled. sample 4: WW CMTP outflow + 18 v/v.% municipal WW (MWW) (days ). 17

18 WW ANAEROBIC DEGRADATION MONITORING 18

19 RESULTS OF WW ANAEROBIC DEGRADATION References for RCF paper mill (Meyer and Edwards, 2014): COD effic.: %, SMP: m 3 t -1 COD degr. 19

20 SLUDGE AND BIOGAS BALANCES WITH WW AN TP Sludge sample Dry Matter Loss of Ignition Net Caloric Value Unit % %s.s. MJ kg -1 s.s. PS DIP AN inflow 53.5± ± ±0.22 PM DIP AN outflow 16.4± ± ±0.54 WAS 17.2± ± ±0.62 HWAS 10.5± ± ±0.44 Anaerobic biomass SLUDGE Parameter Unit Paper mill today ANTP DIP WW ANTP DIP WW without SS + nutrients ANTP CMTP outflow + nutrients ANTP CMTP outflow + MWW BS reduction % / Total mill sludge reduction BIOGAS (BG)/BIOMETHANE (BM) % / BM production m 3 year ,364, ,530 1,248,909 1,362,018 BG energy versus mill total fuel energy consumption Sludge +BG energy versus mill total fuel energy consumption % %

21 AEROBIC TREATMENT OF ANAEROBIC PRE-TREATED WW OBJECTIVE: To determine the effect of the WW AN pre-treatment to overall WWTP efficiency.. Pilot SBR reactor 30 L, with a stirrer and an aeration unit, an inoculum AS from paper mill (20 L), batch mode, several cycles, ph: , O 2 content: mg O 2 L -1. The WW inflow / outflow per batch: 10 L. COD monitoring vs. time WW inflow Filling Aeration Sedimentation Discharge of WW 1. Sample 1: CMTP outflow +nutrients AN pre-treated, 2. Sample 2: CMTP outflow+18%mww AN pre-treated, 3. Sample 3: CMTP outflow +nutrients AN pre-treated + 18% MWW added before aerobic treatment. 21 WW outflow

22 RESULTS OF WW AEROBIC (AERO) TREATMENT Parameter Unit Sample 1 Sample 2 Sample 3 Removal efficiency of WW TP COD - AN % 63.2± ± ±3.4 BOD 5 - AN % 74.4± ±6 79.8±2.4 COD - AERO % 51.3± ± ±8.9 BOD 5 - AERO % 95.5± ± ±3.1 COD - total % 82.2± ± ±2.4 BOD 5 - total % 98.9± ± ±1.0 Efficiency of WWTP with AN pre-treatment of all samples stays at the same level as it is with aerobic TP. SVI (sludge volume index) of WAS is reduced from 186 to 81 ml g -1. The growth of aerobic biomass is 39% and of anaerobic biomass only 3.65% vs. COD removed. 22

23 SAVINGS WITH WW ANAEROBIC TRETMENT (DIP WW without SS + nutrients, CMTP outflow + nutrients, CMTP outflow + MWW) Basis for calculation: Reduction of BOD 5 load on entering the AERO treatment 55-78% Reduction of HRT in aeration from 18 h to min. 3 h Production of BM: 1 to 1.3 million m 3 year -1 1) Reduction in electricity consumption (31-50%), nutrients (17-100%) and process water in the BTP (8-50%). 5) Estimated total savings with the introduction of ANO: t -1 gross pap. 2) BB is fully energy recovered within the paper (reduction amounts to 49-71%). 4) Energy production from sludge: % and from biomethane: % and thus lower consumption of fossil fuels and reduction in CO 2 emissions %. 3) Lower operational costs of BTP by 49 to 58 % (environmental taxes is included). 23

24 Process CONCLUSION OBJECTIVE 1 (WAS reduction amounts to 50%) OBJECTIVE 2 (positive energy balance of sludge) >3,500 MJ t -1 ) AN T WAS 26-33% < 3,500 MJ t -1 AERO T WAS 20-26% < 3,500 MJ t -1 AN T DIP WW AN T DIP WW without SS + nutr. AN T CMTP outflow + nutr. AN T CMTP outflow + 1% HWAS + nutr. AN T CMTP outflow + 18% MWW 59% (52% total biological sludge (BS)) 2,839 MJ t -1 53% (49% total BS) 3,585 MJ t -1 65% (59% total BS) 3,611 MJ t -1 80% (73% total BS) 3,000 MJ t -1 (energy consumption, chemicals) 78 (71% total BS) 3,727 MJ t -1 24

25 WW from the RCF paper production with deinking process is well AN degradable. Conclusions from the investigation suggest that ANAerobic treatment of mill WW after SS elimination and with the addition of MWW is economically and environmentally the best option to improve the mill s internal sludge and WW management situation. ANAerobic treatment reduces the impact of the paper mill on the environment and contributes to the sustainable environmental management. 25

26 THANK YOU FOR YOUR ATTENTION. 26