| Saline organic wastewater is an urgent problem in environmental field because of its huge production,wide sources and complex components.The biological methods with low costs and slight secondary pollutant effects have been widely used in saline organic wastewater treatments.Among them,aerobic granular sludge that was developed in the end of last century has many advantages,including compact structure,excellent settleability,stress resistance ability and diverse microbial community.Therefore,aerobic granular sludge is regarded as a promosing technology for saline organic wastewater treatment.However,in terms of diverse discharged characteristics of saline organic wastewater,aerobic granular sludge still has many problems,including long time for granulation,unclear performance and salt-tolerance mechanisms for withstanding short-term saline shocks,unstable performance for withstanding long-term saline stresses and unstatifactory performance for removing refractory organics in saline wastewater.In terms of problems above,the aims of this study were to use floc sludge as seed to quickly cultivate aerobic granular sludge firstly.Considering the short-term discharged characteristics of saline wastewater,the salt-tolerance performance and mechanism of aerobic granular sludge withstanding short-term saline shocks was investigated.And this study explored heavy metals adsorption ability by aerobic granular sludge after saline shocks.Considering the long-term discharged characteristics of saline wastewater,salt-tolerance performance and mechanism of aerobic granular sludge withstanding long-term saline stresses were explored.Considering technical challenges of refractory organics removal in saline organic wastewater,this study took naphthalene as a typical refractory organic pollutant to improve property of aerobic granular sludge,and to enhance the performance of aerobic granular sludge for naphthalene degradation by means of dosing moderately halophilic bacteria.These findings of great theoretical and practical significance will help fully understand the performance and salt-tolerance mechanisms for saline organic wastewater treatment by aerobic granular sludge.Multiple methods of short settling time(5 min),low aeration rate(3 L/min)and anaerobic idle after filling were carried out to cultivate stable aerobic granular sludge with excellent settleability quickly in the sequence batch reactor(SBR)within 33 d.The relative hydrophobicity(RH)and the integrity coefficient(IC)reached 73.5%and 98.1%,which means aerobic granular sludge had enough strength and aggregative ability.The key to fast granulation could be ascribed to short settling time that could screen sludge with well settleability,and high aeration rate that could stimulate microorganisms within aerobic granular sludge to excrete extracecellar polymeric substance(EPS)to aggregate.Anaerobic idle after filling that could inhibit growth of filamentous bacteria was beneficial to stable aerobic granular sludge.The performance of aerobic granular sludge to withstand short-term saline shocks was evaluated.The results showed that no obvious change of sludge concentration after all saline shocks from 0 to 60 gNaCl/L.Moreover,COD removal efficiencies could revert to 87.5%in short-term recovery during 15 cycles(90 h)after 40 g/L saline shock.However,stable COD removal efficiency(73.8%)could not recover to the previous level after 60 g/L saline shock.These results suggest aerobic granular sludge could withstand up to 40 g/L saline shock.The corresponding salt-tolerance mechanisms could be explained from three aspects.After 40 g/L saline shock,the specific oxygen uptake rate(SOUR)of aerobic granular sludge could recover to ensure biological activity.Aerobic granular sludge with the integrity coefficients of 87.6%maintained compact structure.In addition,aerobic granular sludge with relatively small lactate dehydrogenase(LDH)release of 129.4%,which means cells within aerobic granular sludge has relatively integrated structures.Saline stimulative treatments(NaCl concentration ranged from 0 to 50 g/L)were conducted to enhance Zn2+ adsorption performance by aerobic granular sludge.The results showed that the aerobic granular sludge in response to a 30 g/L saline stimulation exhibited the best adsorption performance,and the adsorptive capacity at equilibrium reached 29.76 mg/g.Moreover,the adsorption isotherm was fitted to Langmuir equation.The calculated maximum adsorption capacity in 30 g/L saline treatment group reached 73.94 mg/g.Analysis of EPS components suggested the enhanced adsorption of aerobic granular sludge might be ascribed to increasing polysaccharides content in the EPS after short-term saline stimulations.Additionally,Fourier transform infrared spectroscopy(FTIR)and X-ray photoelectron spectroscopy(XPS)results indicated hydroxyl groups of EPS were main sites for Zn2+ binding.The study in the performance of aerobic granular sludge withstanding long-term saline stresses was conducted.The results showed that aerobic granular sludge could withstand long-term saline stress,and the maximum salinity reached 50 g/L within 113 d.Under 10 g/L,30 g/L and 50 g/L salinity,COD removal were 90.3%,88.0%and 78.0%respectively,which means aerobic granular sludge had good ability for organic matter removal.Aerobic granular sludge also remained relatively high bioactivity.Aerobic granular sludge had enough strength and aggregative ability under 10 g/L and 30 g/L salinity.IC maintained 96.2%and 97.7%.RH remained 80.5%and 83.8%at the same time.Under 50 g/L salinity,IC and RH decreased to 85.4%and 73.1%respectively,which means the strength and aggregative ability of aerobic granular sludge got a little worse.Nevertheless,aerobic granular sludge could still keep stable.The salt-tolerance mechanisms should be ascribed to overproduction of EPS by non-halophilic bacteria that enhanced sludge aggregation,and the compact structure that ensure the microorganisms bioactivity within aerobic granular sludge to maintain the function of removing organic matters under 10 g/L and 30 g/L salinity.However,the salt-tolerance mechanisms in 50 g/L salinity were that the dominated microbial communities shifted to moderately halophilic bacterium to keep aerobic granular stabilization and organic matters removal.Aerobic granular sludge was applied for naphthalene degradation in saline wastewater,and the enhanced naphthalene degradation was achieved by dosing Martelella sp.AD-3 in the reactor.Naphthalene removal by aerobic granular sludge reached 88.7%under 30 g/L salinity when naphthalene concentration was 15 mg/L.Aerobic granular sludge which withstood naphthalene toxicity could remain bioactivity,integrity and aggregation.When naphthalene concentration reached 25 mg/L,naphthalene removal of aerobic granular sludge decreased to 70.4%.Bioactivity,integrity and aggregation of aerobic granular sludge were affected.The corresponding SOUR,IC and RH decreased to 0.38 mgO2(g VSS)-1min-1,94.0%and 73.5%.Then 3%mass ratio of Martelella sp.AD-3 was dosing into reactor to enhance naphthalene removal.The naphthalene removal increased to 93.6%after reaching a stable stage,while naphthalene removal was 76.8%in control group.Bioaugmentation also improved bioactivity,integrity and aggregation of aerobic granular sludge.The corresponding SOUR,IC and RH recovered to 0.48 mgO2(g VSS)-1min-1,96.3%and 78.3%.The growth of moderate halophilic bacterium Halomonas and Marinicella was promoted by dosing Martelella sp.AD-3 under saline and naphthalene-containing condition.And the abundance of genes for naphthalene degradation increased by dosing Martelella sp.AD-3,which was in favor of naphthalene degradation. |
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