The present invention relates to a method and biomechanical apparatus for treating ship bilge wastes contaminated with petroleum or biodegradable materials. More particularly, the invention relates to a method and apparatus for the physical separation of petroleum hydrocarbons from bilgewater and the subsequent microbiological remediation of the petroleum and biodegradable materials in the ship bilgewater.
The shipping industry and military generate millions of gallons per year of bilgewater contaminated with petroleum hydrocarbon and/or hazardous pollutants. The direct discharge of this contaminated bilgewater from commercial and non-commercial shipping vessels into the world""s oceans and lakes is a universal environmental problem. Currently, the majority of such bilge wastes is processed through on-board oil/water phase separators. The separated oil is either stored in containers or pumped back to the bilge. The separated water is either sent overboard or back in the bilge area. However, the water that is processed by such separators often exceeds international and domestic regulatory standards for legal discharge. Local and international laws impose severe fines and/or imprisonment if ships discharge bilge waste while in harbor areas. Ship owners must dispose of the contaminated bilgewater by costly and inconvenient methods such as pump, haul, and incineration.
On shore, the storage and transportation of such bilge wastes requires countless tanks and pipelines. Substances typically processed and stored at these facilities include petroleum distillates, industrial solvents, and oily bilge wastes. Due to the dangers presented by storing and transporting concentrated solutions of these materials, engineers and government agencies conduct extensive research and development to insure the tanks and pipelines used will effectively and safely contain these materials. Weathering and unforeseen engineering limitations, however, often cause the facilities to fail, resulting in the release of chemicals into the environment from on-shore storage facilities.
The release of concentrated bilge wastes typically cause extensive damage to the local ecosystem by contaminating or killing indigenous plant and animal life. More remote ecosystems may be affected if the contamination migrates away from the site of ship discharge.
U.S. Pat. Nos. 4,072,614, 4,426,293, 5,277,794, 5,609,760, and 5,965,015 disclose methods to process oily water whereby oil is physically separated and removed prior to the discharge of the water phase from the separator system. Commercially available separators typically consist of a tank containing oleophobic filters, coalescing resin beads or hollow fiber membranes. These agents, combined with gravitational forces, separate oil from water. The various filters and beads components can be used individually or in combination to separate petroleum products from the bilgewater thereby insuring the overboard discharge of oil-free water into surrounding waters.
A major problem with these separator technologies is that concentrations of petroleum hydrocarbon contaminants remaining in the water phase often exceed the regulatory-allowed limits for discharge into open waters. The reasons for poor separator performance vary but include the typical presence of engine-cleaning detergents and other substances that emulsify oil into water, thereby allowing a higher percentage of oil to become associated with the aqueous phase. Ship agitation and inefficient phase separators allow significant amounts of petroleum to enter the aqueous phase as well. Also, under circumstances where filter technologies have been employed, these filters typically contain a significant volume of oil; consequently they are not typically capable of providing lengthy unattended service such that oil leakage from the filters can become a significant problem resulting in the overall poor performance of the oil water separator. In general, the operation and maintenance costs associated with oil water separators that utilize filter or coalescing bead technologies can be significant over the life of the unit. The net effect of these events is that relatively high amounts of petroleum can be, and are, discharged directly into the surrounding waters, thereby posing significant environmental risks as cited earlier.
U.S. Pat. Nos. 3,846,290, 4,385,121, 4,765,902, 4,992,174, and 5,080,782 disclose methods for reducing the amount of petroleum hydrocarbons in a solution. Although these methods achieve remediation in soil and groundwater environments, the methods are disadvantageous for cleanup of bilge wastes for a number of reasons. First, the equipment used is often large and cumbersome. This type of equipment would not be appropriate for ship environments because of space constraints often encountered in ships. A second reason pertains to the hydrocarbon-degrading microorganisms used to degrade the contaminants associated with bilgewater. Although indigenous microbial populations may be sufficient in terrestrial environments to biodegrade petroleum hydrocarbons that may have contaminated it, such microorganisms may not be present in the bilge environment. Because the oil/water mixture is periodically removed from the ship as a normal part of cleaning operations, any hydrocarbon-degrading microorganisms, which may be present, would also be removed in the process. Thirdly, terrestrial/groundwater bioreactor systems are not designed to treat oil contaminated with surfactants and cleansers often associated with bilge wastes. And fourthly, hydrocarbon-degrading microorganisms associated with terrestrial environments are typically not efficient degraders in surface water environments (i.e., saltwater).
U.S. Pat. No. 5,248,253 to Behmann describes the use of an onboard-activated sludge bioreactor combined with nutrients obtained from raw sewage (xe2x80x9cblack waterxe2x80x9d from toilets) and wastewater from showers, sinks, and kitchen facilities (xe2x80x9cgrey waterxe2x80x9d) to biodegrade bilge oils. Although the method achieves some reductions of petroleum hydrocarbons, there are several drawbacks of this approach. First, the mixing of xe2x80x9cblackxe2x80x9d and xe2x80x9cgreyxe2x80x9d water to achieve optimal nutrient concentrations in the activated sludge bioreactor is not practical due to the inconsistent amount of nitrogen present in these materials. Second, appropriate concentrations of phosphate are not found in these xe2x80x9cblackxe2x80x9d and xe2x80x9cgreyxe2x80x9d waters to allow complete metabolism of petroleum hydrocarbons to occur. Third, activated sludge systems generate considerable sludge material (i.e., solids) which are cumbersome to deal with and expensive to dispose. Fourth, pathogenic microorganisms are often associated with xe2x80x9cblackxe2x80x9d water wastes which present a risk to both humans and the environment when such water is discharged to open waters.
U.S. Pat. No. 3,938,692 whereby Gutnick et al. describes the application of microorganisms and nutrients to biodegrade residual oil in the emptied cargo compartments. This method involves the addition of microbes rather than the utilization of an on-site bioreactor. There are several limitations of this approach. First, the absence of a bioreactor limits the amount of dissolved oxygen required to complete metabolism of petroleum hydrocarbons. The method of the ""692 patent is essentially an activated sludge batch reactor which is less efficient than continuous flow fixed-film bioreactors for the reasons cited earlier. In addition, the method does not allow control of the amount of hydrocarbon present in any given cargo compartment. High levels of petroleum hydrocarbons may be toxic or indigestible to microorganisms introduced into these compartments, whereas the current invention allows for the control of petroleum hydrocarbon concentrations being treated. Thirdly, there are no provisions for accurately maintaining the required nutrients within the cargo compartment in the method of the ""692 patent.
U.S. Pat. No. 5,807,485 to Caplan and Kelemen addressed the need for a method and apparatus for the bioremediation of bilgewater contaminated with petroleum and hazardous substances. The described apparatus permits continual, efficient treatment of contaminated bilgewater by protecting the treating microbial inoculum from toxic overloading of the contamination, and generating an increased rate of remediation in the bilge waste environment. A potential disadvantage of this system is that it is primarily designed to remediate water previously processed by the shipboard oil-water separator. This reliance on a shipboard oil-water separator could therefore potentially limit the bioremediation apparatus continuous operation time because of the frequent and expected operational downtimes of typical shipboard oil-water separators.
The present invention meets the foregoing needs by providing an apparatus and method for the biological treatment of bilgewater contaminated with a biodegradable material, for example a petroleum product or a hazardous substance, i.e., a substance which may be classified as toxic, corrosive, irritants, flammable or combustible, or generating pressure in the course of decomposition. The basic approach is to treat the contaminated bilge waste using an interactive system comprising, in combination, a pumping system to transfer bilge waste directly from the shipboard bilge compartment or waste oil holding tank into the first compartment of the apparatus which separates the aqueous from non-aqueous (e.g., petroleum or hazardous substances) phases. The non-aqueous phase is transferred to a holding tank for eventual off-site disposal, recycling or on-board incineration. The aqueous phase is then pumped into a vessel, i.e., bioreactor, which removes dissolved constituents of the biodegradable material in the bilgewater. The bioreactor contains a culture of indigenous, genetically engineered, or enriched bacteria. When constructed and operated as disclosed herein the invention provides a fast and efficient means for the physical separation of highly concentrated oily bilge wastes (i.e., petroleum hydrocarbons) from emulsified oily bilgewater and remediating phase-separated contaminated bilgewater.
The apparatus generally includes a piping and pumping system, for the transfer of liquid bilge waste to a chamber or compartment of the apparatus whereby a system of hydrocarbon sensors, level switches, solenoid valve and piping facilitate the separation and transfer of non-aqueous phase material to a collection tank, a pumping and piping system for the transfer of the aqueous phase bilgewater, containing a dispersion of the biodegradable material into a second chamber, i.e., a bioreactor, for treating the transferred bilgewater, and a piping and pumping system for discharging the treated bilgewater either overboard or processed back into the bilge. Preferably, the treated bilgewater is discharged overboard if appropriate cleanup standards are achieved.
Gas and nutrient injection systems maintain the bioreactor, preferably containing viable cultures of microorganisms. The culture of microorganisms comprises microorganisms fixed to a support media in the vessel and microorganisms, arising from those attached to the support media, which slough off and disperse into the recirculating or discharged bilgewater. The microorganisms"" method of attachment to the support media is not completely understood. However, experience and the scientific literature suggest that fixed-bed bioreactor systems are more tolerant to fluctuations in contaminant flow and concentrations than are activated sludge systems. Preferably, the microorganisms fixed to the support media regenerate so as to maintain a substantially constant microbial biomass within the vessel. In contrast to the methods disclosed in the patents discussed above, in the method of the present invention, nutrient concentrations and pH for optimal microbial growth and metabolism of petroleum hydrocarbons may be regulated.
After treatment, the bilgewater contains dissolved gases and nutrients, as well as those microorganisms sloughed off the support media. This treated water can then be discharged into open waters if regulatory standards are achieved or recirculated into the bilge, whereby the sloughed microorganisms act as a seed culture for stimulating in situ remediation of contaminated bilgewater. A secondary benefit of overboard discharging of the microbe-rich effluent from the bioreactor is the possible cleanup of petroleum slicks surrounding the ship.
The process of the present invention may be performed on any ship contaminated by biodegradable materials, including hazardous and non-hazardous substances degradable by microorganisms. Typical biodegradable materials, which may be biologically treated using the process of the invention, include alcohols, aromatics, carbohydrates, ketones, petroleum hydrocarbons, phenols, phthalates, chemical solvents, chlorinated compounds, detergents, and mixtures thereof.
The microbiological treatment means, operated as described herein, may be used to significantly reduce various concentrations of biodegradable materials dissolved in the bilgewater. Further, by integrating the bilge waste pumping system into the apparatus, the microbial culture is substantially protected from toxic overloading of the biodegradable materials. Accordingly, it is possible to continuously treat contaminated bilgewater without supplementing the treating culture to replace microorganisms lost due to the introduction of toxic concentrations of biodegradable materials.