The ArrowBio Process

The ArrowBio Process integrates an innovative, proven, liquid-based separation technology and high-rate anaerobic digestion - eliminating any need for prior separation or classification of mixed waste streams. The following types of wastes can be treated as-received:

Municipal Solid Waste. Unsorted industrial waste from the paper (including recycled paper) and food processing industries. Manures and agricultural residues. Slaughterhouse wastes. Sludge from sewage and water treatment plants. Industrial settling tank sludge. Yard waste/garden trash with or without other household discards

Of these wastes, the most universal, and probably the most problematic, is Unsorted Municipal Solid Waste (MSW). It consists of a myriad of discards from households, businesses, and institutions managed in common. Thus MSW is extremely heterogeneous, seasonally variable, and differing in composition even among different collection routes within a given municipality. The organic and inorganic fractions pose very dissimilar problems, yet are received as a mixture in a single waste stream.

As a severe test of The ArrowBio Process, a realistic scale facility is in operation at the town of Hadera, Israel. Real unsorted MSW is received from that city and processed smoothly.

The fundamental advantage of the ArrowBio Process is two-fold. First, the MSW (or other waste stream) is processed directly as tipped from the collection truck. In the primary stage, organic and inorganic materials are separated through a unique, liquid-based, technology, involving gravitational settling, screening, and hydro-mechanical shredding of organic solids. Whereas ordinary separation schemes suffer from the wetness, or excessive dryness, of MSW, the ArrowBio Process frankly uses liquids to great effect.

The first stage end products are clean recyclables such as glass, metals, and plastic. Items such as batteries are removed gently, without breakage, thereby avoiding leakage of potentially toxic materials. Yet another, intermediary, product is an organic stream now ready for the next, biological, stage. The first stage thus performs two functions, separation and preparation, without additional machinery or effort.

That is, in addition to removing inorganic and other non-biodegradable materials, the liquid-based separation simultaneously conditions the organic material for rapid biological action. This is accomplished by bringing the organic matter into solution or fine suspension (slurry). The solution/suspension is very rich, with a chemical oxygen demand (COD) in the tens of thousands of milligrams per liter. This supports the high-rate transformation of the organic wastes to methane (biogas) by naturally occurring microbial communities, in two highly controlled sequential reactors. Biogas production far exceeds in-house energy needs.

Excess biomass, discharged from the second reactor, is thoroughly stabilized and usable directly as an organic soil amendment ("compost"), or may be upgraded to a value-added product. Excess biologically generated water is either removed from the system (COD in the tens of milligrams per liter) or sent as makeup liquid to the up-front separation stage. Thus, with respect to energy and water, the system is autonomous.

Since it is consumed in producing energy for in-house use and/or export, emission of methane (potent greenhouse gas) to the atmosphere is entirely prevented.

Significant regional differences in MSW composition are noteworthy. In the Middle East and Asia, biodegradable organic matter may comprise 60 to 90% of the waste stream, with the remainder as biologically inert, mostly inorganic, materials. In contrast, European and North American MSW generally contains only 30 to 50% organics. Regardless of organic/inorganic proportion, unsorted MSWs are treatable by The ArrowBio Process.

The ArrowBio Process effortlessly accommodates the increasing tendency, mandated by national or local laws and regulations, to require source-separation of recyclable materials at the household, business, or institution of origin. Resultant shifts in MSW composition pose no problem in the process cycle. Rather, a given facility's capacity is effectively increased by this tendency. Moreover, perfect compliance with such mandates is neither expected nor achievable. Anyway, the function of conditioning the organics for high-rate methane production is indispensable.

Pre-Treatment and Preparation of the Waste The waste is delivered by trucks into the preparation building. This building is equipped with exhaust fans and Bio-Filters, which assure that no smells escape into the environment. The waste is emptied directly into a reception chute and passed through a bag opening unit and a wet shredder. Water, essential for the shredding process, is re-circulated within the plant and no additional water needs to be added. From there the waste is transferred directly into the dissolving tank. Water is added and by imposing high shearing forces, the organic material is disintegrated down to fiber size, forming thin slurry so that it is separated from any inert material. Heavy components like broken glass, batteries, stones, metal parts etc. sink to the bottom and are separated from the slurry via a special discharge chamber.

1st Stage Acidogenic Fermentation The organic slurry is pumped into the first Bio-Reactor or fermentation tank for facultative anaerobic digestion of the organic phase. Naturally occurring microorganisms start the fermentation process and transform the complex organic material into simpler compounds such as organic and fatty acids. Maintaining correct pH and organic material concentration in the reactor, together with proper liquor circulation and hydraulic retention time controls the process. This stage is a continuous process where fresh slurry is fed into the 1st reactor and fermented liquid is drawn off simultaneously and transferred to the 2nd stage.

2nd Stage Anaerobic Methanogenic Fermentation The liquids leaving the 1st stage reactor are rich in organic material in the form of various organic acids. These liquids are being heated to ~40°C and pumped into the second Bio-Reactor for anaerobic degradation of the organic materials and the generation of biogas. Here too, naturally occurring microorganisms perform the degradation process and transform the organic material into biogas (~ 70% CH4 : 30% CO2) and biomass. This process is controlled by maintaining correct pH and organic material concentration in the reactor, together with proper solids concentration in the liquor and correct circulation and hydraulic retention time. This stage is also a continuous process where liquids from the 1st reactor are fed to the 2nd reactor and effluents are removed from the 2nd reactor. These effluents are being recycled within the system in order to maintain proper solids levels in the 1st reactor and for the initial stages of shredding of the incoming waste and the separation of inert material. Basically, no fresh water are added to the system.

The biogas, which is formed in the 2nd reactor, is being collected at the upper part of the reactor by means of a specially designed built-in compartment. This gas is re-circulated by a compressor and re-injected into the 2nd reactor close to its bottom, thus assuring a permanent agitation without mechanical devices. During routine operation, the biogas is also routed out of the system directly to energy generating units as steam boilers or electrical generators. The biogas can also be stored in simple inflating buffer tanks.

Treatment of final Products The biological sludge formed in the 1st and 2nd reactors is drawn off at pre-set periods, dictated by the process control. This sludge contains many plant nutrients as ammonia and phosphorus in a readily available form to the plants. This fraction, called ArrowBio compost, can be dewatered rather simply and sold as a high value soil conditioning agent. Further processing such as pelletization of this product will increase the market potential and value of the ArrowBio compost. The long solid retention time in the 1st and 2nd reactors ensures a fully stabilized product which do not deplete the soil of nutrients due to intrinsic microbial activity and also is free of all pathogenic germs, bacteria, weed seeds, etc.

The biogas generated in the 2nd stage reactor is transported into a gas storage tank via filters which remove excess humidity and trace pollutants such as naturally formed H2S. The biogas is than used as a fuel for water heating, steam generation or electricity generation.

The liquid from the dewatering process of the ArrowBio compost is partly reused for shredding and dissolving the incoming waste. Excess water is stored in a separate tank and is being discharged directly into the public sewage system or into a simple biological treatment plant.

Materials Recovered From The ArrowBio Plant In Operation.   Aluminum Fibers Glass Plastic