Journal of Environmental Engineering

Anaerobic digestion of sludge from a full‐scale biological phosphorus removal (BPR) treatment facility resulted in significant release of soluble phosphorus. However, the increase in phosphorus and/or change in microbial population associated with the BPR conversion had no significant impact on sludge dewatering characteristics. Cationic polymer requirements (Percol 757) for effective sludge conditioning were not significantly impacted by the conversion to BPR treatment. Inorganic chemical addition using both lime and ferric chloride promoted effective sludge conditioning while concurrently promoting the reduction in filtrate phosphorus concentration. Suggestions for implementing the experimental results in full‐scale sludge treatment systems are also presented.

The Corps of Engineers and EPA conducted a feasibility study of using dredges to remove PCBs from the highly contaminated sediments of the New Bedford, Mass., harbor, a Superfund site. Three types of dredges were tested. Also, a confined disposal facility (CDF) was constructed to test the feasibility of onshore containment of the dredged material. Laboratory settling tests and modified elutriate tests were conducted prior to dredging to predict the release of PCBs in the effluent. Comparisons and predictions with field measurements showed that the prediction method was valid and useful for PCBs. The average concentration of dissolved PCB of 4.8 μg/L was close to the prediction of 7.5 μg/L. The average total concentration of 28 μg/L was less than the predicted value of 65 μg/L, because the average effluent suspended solids (SS) of 67 mg/L was less than the predicted 120 mg/L, due to dredge operating problems. Other data showed that dredging is a feasible remediation method.

The experimental in situ aquifer biorestoration site at Moffett Field, California, is a small, confined, sand and gravel aquifer, interspersed with layers of silts and clays. Laboratory sorption and solids characterization studies were carried out on core material recovered from in and around the aquifer zone. Equilibrium (distribution coefficient $K_d$) and nonequilibrium (effective pore‐diffusion coefficient $D_p$) sorption parameters, estimated from batch experiments, were used in one‐dimensional simulations of the breakthrough of three halogenated organic compounds: trichloroethylene (TCE), carbon tetrachloride (CT), and vinyl chloride (VC). Three types of transport models were used: equilibrium partitioning, spherical diffusion, and equivalent first‐order diffusion. The hydrodynamic parameters (dispersion coefficient and pore water velocity) were determined previously using field‐scale tracer tests. Simulations reconfirmed the theory that while an accurate $K_d$ value is required for each compound, it is sufficient, for similar compounds, to measure the rate parameters for one compound, then calculate these parameters for the other compounds. Although the simulations were generally successful, difficulty in estimating the field particle size, and a lack of understanding of field‐scale heterogeneities, limited the accuracy of the simulations and the potential for model verification.

Twenty‐three different sewage sludges were studied to adapt indigenous sulfur‐oxidizing microflora to solubilize a substantial part of trace metals from the sludges. The results showed that the oxidation of elemental sulfur into sulfuric acid with indigenous sludge thiobacilli causes a sludge acidification, lowering the pH below 2.0. This pH reduction solubilizes trace metals to a level compatible with recommended norms for agricultural use with the following metal solubilization efficiencies: Cd, $82\pm 13\%;$ Cr, $31\pm 19\%;$ Cu, $75\pm 21\%;$ Mn, $92\pm 7\%;$ Ni, $70\pm 16\%;$ Pb, $27\pm 21\%;$ and Zn, $85\pm 10\%\text{.}$ The adaptation of this microflora reduces the trace‐metal‐leaching period to 1.5 to five days, depending on the sludge used. The growth and metal‐leaching capacity of the adapted micro‐flora, which is a mixed culture of thiobacilli, was not significantly influenced by the sludge type (nondigested sludge, aerobically or anaerobically digested sludge) and by sludge total solids content.

Zebra mussels adhere tenaciously and gregariously to hard surfaces, thereby fouling water‐processing facilities and equipment. At present, there are few data on zebra mussel adhesion strength to common substrates. A rotating disk test system (RDTS) was used to measure the adhesion strength of small mussels $(\approx 1\mathrm{mm})$ to four materials [polyvinylchloride (PVC), polymethylmethacrylate (PMMA), stainless steel (SS), and aluminum (AL)].

Adhesion strength varied significantly with material but only marginally with residence time (one, two, seven, 14, 21, and 28 days). The estimated shear stress required to remove 95% of mussels $\left({\tau }_{95\%}\right)$ averaged $62\pm 5\mathrm{Pa}$ ($\mathrm{mean}\pm \mathrm{standard}$ error, $n=6$ disks) on PVC, $50\pm 3\mathrm{Pa}$ on PMMA, $48\pm 4\mathrm{Pa}$ on SS, and $31\pm 1(n=4)\mathrm{Pa}$ on AL. ${\tau }_{95\%}$ peaked on the second day (85 Pa on PVC, 65 Pa on PMMA, 57.5 Pa on SS, 32.5 Pa on AL), then decreased to a constant level. Ultimately, this research should provide insight into material selection and designs that minimize attachment and facilitate removal of zebra mussels.

With today's integrated waste management plans, many communities are looking seriously at material and energy recovery from municipal solid waste. Uncertainties that exist include the effectiveness of unit processes for metals removal and future regulations of heavy metals, especially in combustion processes in both the combustion gases and the ash. From the summer of 1988 to the fall of 1989 refuse‐derived fuel and various residue streams from refuse processing were tested for their elemental compositions at the municipal solid waste (MSW) refuse‐derived fuel (RDF) plants at Madison, Wis. and Hartford, Conn. The results indicate that refuse processing at both plants reduces concentrations of most of the 27 elements tested and their flow to the combustion process in the RDF product, compared to their flow in raw or incoming refuse. Each element must be looked at individually, however, regarding the extent of its diversion and the effectiveness of the various processes in partitioning that element.

The activity of biomass in a longitudinal laboratory‐scale rotating biological contactor (RBC) system used for the treatment of evaporator condensate from a sulfite pulping process was determined by chemical parameters (TKN:SS and VSS:SS) and biological kinetic parameters (the rate of endogenous respiration, the maximum specific respiration rate, etc.) carried out in Warburg experiments. The results show that kinetic parameters are more effective in describing the activity of the biomass, both on the disks and in the basin of the RBC, than chemical parameters. The biomass on the disks at the transition phase of carbonaceous removal to beginning of nitrification has a high activity, which is comparable to that of activated sludge with high F/M ratio of 0.9 kg ${\mathrm{BOD}}_5/\mathrm{kg}$ MLSS/day. The biomass suspended in the basin of the RBC has only about one‐tenth of the metabolic activity of the disk biomass.

The need for selective sorption of trace concentrations of toxic Se(IV) and As(V) oxyanions, especially in the presence of competing high concentrations of sulfate ions, is well recognized. In this regard, previous investigators have shown the advantages as well as shortcomings of the fixed‐bed sorption process when activated alumina or strong‐base polymeric anion exchangers are used as sorbents. The present study reports the sorption behaviors of a newly identified sorbent that, in terms of composition, is a specialty chelating polymer with immobilized Cu(II) present at the sorption sites. Experimental results with the new sorbent show higher selenite and arsenate selectivities over competing sulfate ions. Anion exchange accompanied by Lewis acid‐base interactions are the underlying reasons for the new sorbent's enhanced affinities toward arsenates and selenites. In several ways, the new sorbent can complement the shortcomings of activated alumina and other strong‐base anion exchangers.

Backwashing of deep bed filters is achieved by fluidizing the filter media. A mathematical model for velocity gradient in two‐dimensional turbulent flow that can also be applied to flow in fluidized beds in the transitional state was developed. The theory of fluidization in a circular cross‐section column was presented. The existence of a viscous sublayer around each fluidized solid particle and the laminar sublayer thickness at the wall were neglected. To evaluate the theoretical expressions, numerical applications are carried out for filter‐bed materials of two different types of sands and anthracite coal. An indirect verification of the existence of an optimum porosity around 0.70‐0.75 during filter backwashing was observed in the laboratory experiments. The velocity gradient in backwashing of granular filters was found to be a function of power dissipation in a unit volume and coefficient C that indicates the effect of turbulence in total power dissipation. It was also found that turbulence intensity decreases with an increase of porosity, and the arithmetic mean shear stress has a maximum value between porosity values of 0.70 and 0.75.

Uncertainties are unavoidable in water‐quality modeling and subsequent management decisions. Monte Carlo simulation and first‐order uncertainty analysis (involving linearization at central values of the uncertain variables) have been frequently used to estimate probability distributions for water‐quality model output due to their simplicity. Each method has its drawbacks: Monte Carlo simulation's is mainly computational time; and first‐order analysis' are mainly questions of accuracy and representativeness, especially for nonlinear systems and extreme conditions. An improved (advanced) first‐order method is presented, where the linearization point varies to match the output level whose exceedance probability is sought. The advanced first‐order method is tested on the Streeter‐Phelps equation to estimate the probability distribution of critical dissolved‐oxygen deficit and critical dissolved oxygen using two hypothetical examples from the literature. The advanced first‐order method provides a close approximation of the exceedance probability for the Streeter‐Phelps model output estimated by Monte Carlo simulation using less computer time—by two orders of magnitude—regardless of the probability distributions assumed for the uncertain model parameters.

Biological solubilization of metals of anaerobic sludge samples was performed in Erlenmeyer flask experiments, comparing two sources of the FeSO₄·7H₂O substrate. There was no difference in the growth of Thiobacillus ferrooxidans using either laboratory grade FeSO₄·7H₂O or a metallurgical industry by-product. The relatively low levels of metals in the metallurgical residue do not interfere with the decontamination process, for sludge originating from a municipal wastewater-treatment facility. In addition, use of this source offers substantial economic benefits. Commercial substrate averages $13,000 U.S./t, compared to $43 U.S./t for the industrial product; more than a 300-fold difference. Using this source of substrate, biological solubilization would cost approxiately $10 U.S./t dry sludge, or 11 cents/m³ of treated water for a plant treating 388,000 m³/day. This is significantly less than the cost of incineration ($300 U.S./dry t). Biological solubilization is therefore a promising alternative to traditional methods of sludge treatment.

The form of nitrogen influences the yield of microorganisms from a given amount of substrate. Previous work on calculating yields from thermodynamic principles is modified to give a correct account for the form of nitrogen. Nitrogen in the reduced form of ammonia contributes energy toward cell synthesis while the more highly oxidized forms of nitrogen require an expenditure of energy. In addition, the electron equivalency of cells changes depending on the form of nitrogen available to the microorganisms. These principles are incorporated into two approaches that yield equivalent results to formulate the overall reaction stoichiometry for substrate, nitrogen source, cells, and other products based on bioenergetics. An example is given where the change of nitrogen source from nitrate to ammonia results in an increase in cell yield of 29%.