Equilibrium and kinetic modelling of Cd(II) biosorption by algae Gelidium and agar extraction algal waste

In this study an industrial algal waste from agar extraction has been used as an inexpensive and effective biosorbent for cadmium (II) removal from aqueous solutions. This biosorbent was compared with the algae Gelidium itself, which is the raw material for agar extraction. Equilibrium data follow both Langmuir and Redlich-Peterson models. The parameters of Langmuir equilibrium model are q(max)=18.0 mgg(-1), b=0.19 mgl(-1) and q(max)=9.7 mgg(-1), b=0.16 mgl(-1), respectively for Gelidium and the algal waste. Kinetic experiments were conducted at initial Cd(II) concentrations in the range 6-91 mgl(-1). Data were fitted to pseudo-first- and second-order Lagergren models. For an initial Cd(II) concentration of 91 mgl(-1) the parameters of the pseudo-first-order Lagergren model are k(1,ads)=0.17 and 0.87 min(-1); q(eq)=16.3 and 8.7 mgg(-1), respectively, for Gelidium and algal waste. Kinetic constants vary with the initial metal concentration. The adsorptive behaviour of biosorbent particles was modelled using a batch reactor mass transfer kinetic model. The model successfully predicts Cd(II) concentration profiles and provides significant insights on the biosorbents performance. The homogeneous diffusivity, D(h), is in the range 0.5-2.2 x10(-8) and 2.1-10.4 x10(-8)cm(2)s(-1), respectively, for Gelidium and algal waste.     

Bioremoval of cadmium from aqueous solution by black gram husk (Cicer arientinum)

Husk of black gram (Cicer arientinum), a waste of no commercial value, was investigated as a new biosorbent of cadmium from low concentration aqueous solutions. With 99.99% sorption efficiency from 10mg l(-1) cadmium solution, the biomass required at saturation was 0.8 g mg(-1) cadmium. Biosorption was rapid and equilibrium was achieved in 30 min. Among the various desorbing agents tested, 99.89% cadmium recovery was achieved with 0.1M HCl. Sorption efficiency of cadmium during six biosorption-desorption cycles in batch operations declined, which was traceable to 39.0% black gram husk (bgh) weight loss. This decline was only 9.71% when compensated for biomass loss, which is comparable to 10.45% decline during six cycles in fixed bed column bioreactor in which biomass loss was only 5.98%. On plotting breakthrough curves it was noted that bgh in the fixed bed column was capable of bringing down cadmium concentration from 10 to 0.1 mg l(-1) in 35.5 l volume. Biosorption of cadmium was not effected in the presence of other cations. Comprehensive characterization of parameters indicate bgh to be an excellent material for biosorption of cadmium to treat wastewaters containing low concentration of the metal. As an agrowaste, the advantage of application of this material as a metal biosorbent in a fixed bed column bioreactor system, in comparison with those based on immobilized algae or biomass of algal, fungal and bacterial origin, is considered.     

Derivation and application of a new model for heavy metal biosorption by algae

An equilibrium model for describing the relationships between important parameters for heavy metal sorption by algae was derived through a thermodynamics approach. In this model, both the removal efficiency of heavy metal and metal adsorption per unit algal biomass are considered to be simple functions of the ratio of algal biomass concentration to the initial metal concentration for selected conditions, i.e. as at constant pH and temperature. The model was found to fit the experimental results well (judged by the correlation-regression coefficient, R2), for the adsorption of cadmium, copper, lead and zinc by two algal species, Oocystis sp. (both living and non-living) and Chlorococcum sp. The applicability of the model was also supported by the reprocessed results of experimental data given in the literature, i.e. for the metal species, Cd, Pb, Cu and Ag, the algal species, Chlorella vulgaris, Scenedesmus quadricauda and Cladophora crispata, and both batch and continuous fixed-bed reactors. It was also demonstrated that the model could be applied over a broad range of pH for cadmium and copper adsorption by Oocystis sp. However, the model was not applicable at very low and high pH levels, due to negligible adsorption and precipitation, respectively.     

The effect of bacterial contamination on the heterotrophic cultivation of Chlorella pyrenoidosa in wastewater from the production of soybean products

This study examined the impacts of bacteria on the algal biomass, lipid content and efficiency of wastewater treatment during the heterotrophic cultivation of Chlorella pyrenoidosa. Our results showed that soybean-processing wastewater can enhance the accumulation of lipids in algal cells and thus raise the lipid yield in the pure culture. The bacteria coexisting with algae improved the degradation of total nitrogen (TN), total phosphorus (TP), glucose and chemical oxygen demand (COD). Although the biomass productivity of algae was not significantly affected, the total algal lipid content and lipid production rate were slightly reduced when bacteria coexisted with algae. The difference in the compositions of the medium is presumed to be the main contributing factor for the variation in total lipid content in presence and absence of bacteria. The TN, TP, and COD decreased during the assimilatory process undertaken by C. pyrenoidosa, and the removal efficiency of TN by bacteria depended on the type of nitrogen species in the medium. Additionally, the apparent interaction between the bacterial and algal cultures varied with the changes in experimental conditions. Algae could compete with bacteria for the carbon and energy sources, and inhibit the growth of the bacteria in the presence of high organic matter concentration in the medium.     

Recycling algae to improve species control and harvest efficiency from a high rate algal pond

This paper investigates the influence of recycling gravity harvested algae on species dominance and harvest efficiency in wastewater treatment High Rate Algal Ponds (HRAP). Two identical pilot-scale HRAPs were operated over one year either with (HRAP_r) or without (HRAP_c) harvested algal biomass recycling. Algae were harvested from the HRAP effluent in algal settling cones (ASCs) and harvest efficiency was compared to settlability in Imhoff cones five times a week. A microscopic image analysis technique was developed to determine relative algal dominance based on biovolume and was conducted once a month. Recycling of harvested algal biomass back to the HRAP_r maintained the dominance of a single readily settleable algal species (Pediastrum sp.) at >90% over one year (compared to the control with only 53%). Increased dominance of Pediastrum sp. greatly improved the efficiency of algal harvest (annual average of >85% harvest for the HRAP_r compared with ∼60% for the control). Imhoff cone experiments demonstrated that algal settleability was influenced by both the dominance of Pediastrum sp. and the species composition of remaining algae. Algal biomass recycling increased the average size of Pediastrum sp. colonies by 13-30% by increasing mean cell residence time. These results indicate that recycling gravity harvested algae could be a simple and effective operational strategy to maintain the dominance of readily settleable algal species, and enhance algal harvest by gravity sedimentation.     

Removal and recovery of uranium from aqueous solutions by Trichoderma harzianum

Removal and recovery of uranium from dilute aqueous solutions by indigenously isolated viable and non-viable fungus (Trichoderma harzianum) and algae (RD256, RD257) was studied by performing biosorption-desorption tests. Fungal strain was found comparatively better candidate for uranium biosorption than algae. The process was highly pH dependent. At optimized experimental parameters, the maximum uranium biosorption capacity of T. harzianum was 612 mg U g(-1) whereas maximum values of uranium biosorption capacity exhibited by algal strains (RD256 and RD257) were 354 and 408 mg U g(-1) and much higher in comparison with commercially available resins (Dowex-SBR-P and IRA-400). Uranium biosorption by algae followed Langmuir model while fungus exhibited a more complex multilayer phenomenon of biosorption and followed pseudo-second-order kinetics. Mass balance studies revealed that uranium recovery was 99.9%, for T. harzianum, and 97.1 and 95.3% for RD256 and RD257, respectively, by 0.1M Hydrochloric acid which regenerated the uranium-free cell biomass facilitating the sorption-desorption cycles for better economic feasibility.     

Short-term harmful effects of unionised ammonia on natural populations of Moina micrura and Brachionus rubens in a deep waste treatment pond

Populations of Moina micrura and Brachionus rubens in a deep waste treatment pond were exposed to the natural short-term fluctuations of unionised ammonia (90-min intervals of monitoring) that occur in the course of a day during a summer algal bloom. Under natural conditions, three replicate experiments were conducted in which water temperature, pH, dissolved oxygen, total ammonia, unionised ammonia, phytoplankton biomass and zooplankton (number of living and dead organisms, mortality rate and instant mortality) were studied. The time-course of unionised ammonia concentration was consistent with those shown by temperature, pH, phytoplankton biomass, dissolved oxygen, Moina micrura mortality and Brachionus rubens mortality. On the other hand, temperature, pH and dissolved oxygen never exceeded the tolerance ranges described for Moina and Brachionus, which led us to attribute the cause of zooplankton mortality to unionised ammonia toxicity. Mortality rates of 63%, 27% and 34% were recorded for Moina in each replicate experiment. Brachionus was less affected, with mortalities of 7.3%, 6.2% and 6.0%.These results confirm previous field observations (Water Res. 34(14) (2000) 3666; Water Res. 37(5) (2003) 1048) that attributed a reduction in zooplankton biomass during certain periods of summer (algal blooms) to a harmful side-effect of an excessive increase in phytoplankton biomass: high photosynthetic activity during these periods of proliferation of algae gives rise to an increased pH (>/=8) and, subsequently, leads to production of unionised ammonia (toxic for aquatic organisms) from its ionised fraction.     

Biological leaching of Mn,Al, Zn,Cu and Ti in an anaerobic sewage sludge effectuated by Thiobacillus ferrooxidans and its effect on metal partitioning

The chemical fractionation and bioleaching of Mn, Al, Zn, Cu and Ti in municipal sewage sludge were investigated using Thiobacillus ferrooxidans as leaching microorganism. As a result of the bacterial activity, ORP increase and pH reduction were observed. Metal solubilization was accomplished only in experimental systems supplemented with energy source (Fe(II)). The solubilization efficiency approached approximately 80% for Mn and Zn, 24% for Cu, 10% for Al and 0.2% for Ti. The chemical fractionation of Mn, Al, Zn, Cu and Ti was investigated using a five-step sequential extraction procedure employing KNO3, KF, Na4P2O7, EDTA and HNO3. The results show that the bioleaching process affected the partitioning of Mn and Zn, increasing its percentage of elution in the KNO3 fraction while reducing it in the KF, Na4P2O7 and EDTA fractions. No significant effect was detected on the partitioning of Cu and Al. However, quantitatively the metals Mn, Zn, Cu and Al were extracted with higher efficiency after the bacterial activity. Titanium was unaffected by the bioleaching process in both qualitative and quantitative aspects.     

Binding of Cu(II) to algae in a metal buffer

The interactions of Cu(II) with algal surfaces and exudates were studied in metal-NTA buffers by a combination of several analytical techniques. Suspensions of living algae in the presence of NTA were titrated at constant pH with Cu(II). The various Cu species were determined as follows: a copper ion selective electrode was used reliably in the pCu range 9–12; differential pulse polarography was used to measure separately Cu(II)-NTA complexes and labile Cu(II) species and to evaluate the complexation of copper by ligands in solution; copper bound to the algal surfaces was extracted by acid treatment and measured by AAS. Thus, we determined both the binding of Cu to the algal surfaces and to exudates excreted by the algae. The results were interpreted in terms of conditional equilibrium constants valid at a given pH; the conditional constants, both for the binding to the surfaces and with the exudates increase in the pH range 5.0–6.5. Simple equilibrium models using the experimentally determined binding capacities and equilibrium constants were able to simulate the results and to evaluate the speciation of copper. Under the experimental conditions used, the binding of Cu(II) to algal exudates has a more significant effect on copper speciation than the binding to the algal surfaces. These extracellular ligands may play an important role in decreasing the concentration of free copper ion and thus mitigating the potential toxic effects in organisms.     

Association of polychlorinated biphenyls (PCBs) with live algae and total lipids in rivers-a field-based approach

The association of PCBs and live algal cells in rivers was studied at four locations during four seasons in two Wisconsin rivers. Positive relations between particle-associated PCBs and both chlorophyll-a and algal carbon concentrations indicated that live algal cells were a significant sorption phase for dissolved PCBs. Large Pennate diatoms (Navicula, Synedra, Pinnularia, Diatoma, and Cocconeis), or more rarely, Euglenoids (Trachelomonas sp.), dominated most sample assemblages on an algal carbon basis. These assemblages made up the highest percentage of total SOC during spring (average=50%) and lowest during summer (average=15%). At the three impounded sites, most individual PCB congeners were relatively enriched in samples characterized by: (1) high concentrations of algal carbon (as a percent of SOC), (2) algal assemblages dominated (or co-dominated) by Euglenoids, and (3) high concentrations of total lipids. Despite relatively higher masses of sorbed PCBs in the most lipid-rich samples, there was no robust correlation between total lipid content and particle-associated PCBs when aggregating all samples from the study. A possible explanation is that PCBs are associated with other structural components in live algae and (or) departure from chemical equilibrium in the river due to algal growth kinetics. A kinetic uptake model was used to calculate the mass of PCBs associated with the total organic carbon content of live algae. Based on this model, PCBs were enriched in algal cells during bloom seasons (spring and fall) compared to non-bloom seasons (summer and winter). Further, although individual PCB congener partition coefficients (log) to live algal cells (range=5.3-6.4) overlapped to those for detritus (range=3.6-7.4), PCBs tended to be enriched in detrital carbon pools during non-bloom conditions. The larger range of estimated PCB partition coefficients for detritus likely reflects the more heterogeneous nature of this material compared to live algal cells.     

Treatment of fish-processing wastewater by co-culture of Candida rugopelliculosa and Brachionus plicatilis

This research was conducted as a part of the continuous development of a novel technique for managing fish-processing wastewater by cultivating proteolytic yeast, Candida rugopelliculosa, as possible diet of the rotifer, Brachionus plicatilis. It was feasible to use Alaska Pollack processing wastewater as a growth medium for C. rugopelliculosa, which was stimulatory for growth of the rotifer by 18.3% over the commercial diet of Saccharomyces cerevisiae. Maximum growth of C. rugopelliculosa and reduction of influent soluble chemical oxygen demand (SCOD) concentration were respectively (6.09+/-0.04)x10(6) cells/ml and 70.0% at 6.3h hydraulic retention time (HRT).Method of 4th order Runge-Kutta approximation was successfully applied to determine the Monod kinetics of C. rugopelliculosa by using unsteady state data from only one continuous unsteady state operation at a fixed HRT. The maximum microbial growth rates, mu(max), and half saturation coefficient, K(s), were determined to be 0.82+/-0.22 h(-1) and 690+/-220 mg SCOD/L, respectively. The microbial yield coefficient, Y, and microbial decay rate coefficient, k(d), were determined to be (1.39+/-0.22)x10(4) cells/mg SCOD and 0.06+/-0.01 h(-1), respectively.     

Residual heavy metal removal by an algae-intermittent sand filtration system

A laboratory scale study was undertaken to determine the feasibility of using algae growing in wastewater lagoons to absorb residual heavy metals for subsequent complete removal by intermittent sand filtration of the metal laden algae. In semi-continuous cultures the mixed algal flora native to wastewater lagoons absorbed 70–90% of the cadmium and copper from the wastewater media. Chromium absorption was less by ratio (20% was absorbed), but the mass of chromium removed was much greater as high levels of chromium were added. Only one alga (Oscillatoria sp.) which was extremely resistant to chromium grew in the chromium exposed cultures. Nearly total removal of the cadmium and copper was achieved by the algae-intermittent sand filter system. The net chromium removal agreed with the accumulation analyses.The technical feasibility of removing certain heavy metals from wastewater with such a system was established. However, in depth laboratory and field studies must be conducted to maximize system efficiency, demonstrate tactical limitations, and establish design specifications.     

Helminth eggs inactivation efficiency by faecal sludge dewatering and co-composting in tropical climates

This study investigates helminth eggs removal and inactivation efficiency in a treatment process combining faecal sludge (FS) dewatering and subsequent co-composting with organic solid waste as a function of windrow turning frequency. Fresh public toilet sludge and septage mixed at a 1:2 ratio were dewatered on a drying bed. Biosolids with initial loads of 25-83 helminth eggs/g total solids (TS) were mixed with solid waste as bulking material for co-composting at a 1:2 volume ratio. Two replicate sets of compost heaps were mounted in parallel and turned at different frequencies during the active composting period: (i) once every 3 days and (ii) once every 10 days. Turning frequency had no effect on helminth eggs removal efficiency. In both setups, helminth eggs were reduced to <1 viable egg/g TS, thereby complying with the WHO guidelines 2006 for the safe reuse of FS.     

Effect of Pseudokirchneriella subcapitata (Chlorophyceae) exudates on metal toxicity and colloid aggregation

The effects of Pseudokirchneriella subcapitata exudates on the acute toxicity of metals (Cd, Cu, Pb and Zn) were studied using (1h) algal photosynthesis inhibition tests. The metal concentrations tested were 30, 60, 120, 250 and 500microgL(-1) for Cd and Zn; and 500, 1000, 2000, 3000, 4000microgL(-1) for Cu and Pb. It was established that P. subcapitata exudates markedly decreased metal toxicity. This effect was ascribed to: (i) the presence of organic ligands that bind metals and reduce the concentration of free ionic metal, and/or (ii) interaction of exudates with the cell surface with a subsequent decrease in metal uptake. The effects of the exudates on colloid aggregation were also examined using two different types of single particle counters (SPC). Exudates facilitated the colloid removal, likely via acceleration of aggregation (bridging). The results clearly demonstrate that algal exudates play an important role in the biogeochemical cycling of metals in natural surface water: (1) by reducing free metal concentrations and toxicity to living organisms and (2) by favoring colloid aggregation leading to the removal of colloid-bound metals (colloidal pumping). Such results highlight one potential application of the algae in the remediation of metal-contaminated waters. The results also suggest that current algal toxicity testing protocols, in particular long-term and static tests, may underestimate metal toxicity because of the presence of algal exudates.     

Kinetic characterisation of an enriched Nitrospira culture with comparison to Nitrobacter

Nitrospira and Nitrobacter are nitrite-oxidising bacteria commonly identified in nitrogen removal wastewater treatment plants. Little is known about the growth parameters of Nitrospira or the effects of environmental conditions or inhibitory compounds on Nitrospira activity. These bacterial properties were investigated using an enriched Nitrospira culture and an enriched Nitrobacter culture or Nitrobacter literature values. Compared to Nitrobacter, Nitrospira was found to have a comparable optimal pH range (8.0-8.3); similar normalised activity-temperature relationship (0.44e(0.055(T-15))) for temperatures between 15 and 30 degrees C and a similar oxygen half-saturation constant, K(O) (0.54+/-0.14 mgL(-1)). The major differences identified were that Nitrospira had a lower nitrite half-saturation constant, K(S) (0.9+/-0.07 mgNO(2)-NL(-1)); lower inhibition threshold concentrations for free ammonia (between 0.04 and 0.08 mg NH(3)-NL(-1)) and free nitrous acid (less than 0.03 mg HNO(2)-NL(-1)) and a higher yield (0.15+/-0.04 g VSS g N(-1)). Therefore, Nitrospira is more likely to dominate nitrite oxidation under conditions with low ammonium and nitrite concentrations, which would provide an advantage to them due to their lower K(S) value while avoiding any free ammonia or free nitrous acid inhibition.     

Sorption of copper by olive mill residues

A study on olive mill residues (OMR) as copper adsorbing material is reported in this work. A rough characterization of this waste material has been performed, by microanalysis and SEM pictures. Sorption tests with suspended OMR evidenced copper removal from solution, of about 60% in the investigated experimental conditions. The COD release in solution was also monitored during biosorption. Considering that it was significant, OMR washings with water were performed before biosorption. In this case the COD release in solution was reduced to less than 600 mg/L after two washings, while the OMR metal sorption properties did not change. Regenerated residues by acid solutions gave a copper removal of about 40%, in the same experimental conditions of the first adsorption test: regeneration with EDTA at different concentrations suggested that it presents a damage of adsorption active sites. On the other hand, the use of HCl and CaCl₂ led to completely regenerate the biosorbent material. Tests were also performed with a column filled with 80 g of OMR and the breakpoint was demonstrated to take place after that about 1 L solution was treated in the investigated experimental conditions. Regeneration tests permitted to demonstrate that a concentration factor of about 2 can be obtained in no-optimized conditions, highlighting the possibility of using OMR for the treatment of metal bearing effluents. The main advantage of the process would be the ‘‘low cost’’ biosorbing material, considering that it represents a waste in the olive oil production.     

New biosorbent materials for heavy metal removal: product development guided by active site characterization

Olive pomace wastes were used as precursors for the development of new biosorbents for heavy metals. Thermal and/or chemical treatments were addressed in terms of their effects on functional group properties and copper removal. Product development was guided by experimental characterization (potentiometric titrations, IR spectra, copper biosorption, total surface area) and theoretical modeling of acid-base properties. Olive pomace was characterized by negative charge due to dissociation of two weakly acidic sites (carboxylic and phenolic). After thermal treatment, a char-like material was obtained, characterized by basic sites with positive charge in the acidic pH range. Copper biosorption properties of this material were improved with respect to olive pomace due to the binding ability of pyrone-like sites. Both native and carbonized olive pomace samples were chemically treated by HNO(3). Experimental tests were performed according to factorial designs and analysis of variance was used to evaluate significant effects on copper removal of both oxidant concentration and temperature. Chemical treatment by HNO(3) of carbonized material developed negatively charged groups in the acidic pH range (carboxylic groups), but presented a decreased copper removal. Chemical treatment by HNO(3) of olive pomace without carbonization gave biosorbents with acid-base properties similar to those of native olive pomace, but with a significant increase of copper biosorption. Specific carboxylic-copper interactions indicated by IR spectra and increased surface area due to chemical treatment were simultaneously responsible for such improvement.     

Inorganic nitrogen removal in a combined tertiary treatment—marine aquaculture system—I. Removal efficiences

The increasing awareness that nitrogen is often a key nutrient controlling algal growth in coastal marine waters has led to a concerted effort to find ways to remove ammonia and nitrate from wastewaters. A novel approach to this problem involves the combining of algal and seaweed nutrient stripping processes with a marine aquaculture. Not only is nitrogen removed from wastewater, but important commercial shellfish and seaweeds are produced.A prototype process consisting of growth systems for marine algae, oysters and seaweed, joined in series, was fed secondarily treated wastewater, diluted 1:4 with seawater, for 11 weeks during the Summer of 1972. During this time 95 per cent of the influent inorganic nitrogen was removed by algal assimilation. The oysters in turn removed 85 per cent of the algae, but regenerated as soluble ammonia 16–18 per cent of the nitrogen originally bound in the algal cells. All of the regenerated nitrogen was removed in the seaweed system so that the total inorganic nitrogen removal efficiency of the system was 95 per cent. Phosphorus removal on the other hand was not nearly as complete as only 45–60 per cent was removed.The process has the capability of being expanded to include additional trophic levels in an integrated and highly controlled food chain system to serve the dual function of tertiary wastewater treatment and waste recycling through the production of shellfish and seaweeds.     

Algae and crustaceans as indicators of bioactivity of industrial wastes

Freshwater (Selenastrum capricornutum) and marine (Skeletonema costatum) algae were exposed to liquid wastes from 10 industrial sites in laboratory bioassays. All wastes affected algal growth, either by stimulation only or by stimulation at low concentrations and inhibition at high concentrations. Generally, S. capricornutum and Sk. costatum responded similarly to each waste: SC20's (concentration that stimulated growth by 20%) were between 0.01 and 20.0% waste; EC50's (concentration that inhibited growth by 50%), between 5.1 and 85.5% waste. Since toxicity to S. capricornutum was usually lost by the sixth or seventh day of exposure in all wastes except one, it is recommended that algal tests be carried out for 4 days. Both algal species were more sensitive to the wastes than were Daphnia magna (freshwater) and Mysidopsis bahia (marine). Only three wastes were toxic to D. magna and two were toxic to M. bahia. SC20 and EC50 values are used to calculate the 7-day, 10-year flow rate of the receiving stream required for dilution of effluents to non-toxic concentrations.     

建筑垃圾再生材料灰土挤密桩成桩应用试验

为了掌握建筑垃圾再生材料在灰土挤密桩处理湿陷性黄土地基中的应用性能,首先通过材料力学性能试验确定了粒径为0～30 mm、建筑垃圾与灰土比例为72:28的建筑垃圾灰土挤密桩填料。然后完成了4组不同距径比的试桩应用试验,得到了不同距径比下的桩间土湿陷系数、桩间土挤密系数、桩间土静力触探曲线、复合地基荷载-沉降曲线等应用性能参数及特点。结果表明:桩间距越大,桩间土湿陷性系数越小; 距径比越小,桩间土挤密系数越大,桩间土的比贯入阻力越大; 在试验路段采用距径比2.25的建筑垃圾灰土挤密桩方案时,桩身容许承载力为175 kPa,复合地基承载力特征值为260 kPa,挤密效果良好; 成桩7 d浸水试验后复合地基承载力和桩身承载力平均下降14.3%,但仍满足桩设计要求; 研究结果验证了建筑垃圾再生材料灰土挤密桩处理湿陷性黄土地基的可行性,为工程应用提供性能参数参考,可进一步扩大建筑垃圾的使用范围。