WO1998025858A1

WO1998025858A1 - Closed-loop wastewater treatment system

Info

Publication number: WO1998025858A1
Application number: PCT/US1997/023230
Authority: WO
Inventors: Mansour Mashayekhi; Bradford M. Kane
Original assignee: Alliedsignal Inc.
Priority date: 1996-12-13
Filing date: 1997-12-12
Publication date: 1998-06-18
Also published as: AU5704498A

Abstract

A closed-loop wastewater treatment system subjects untreated wastewater to a series of treatment processes until a desired water quality is achieved. During primary treatment, total suspended solids, heavy metals and inorganic compounds are removed. Biodegradable components are thereafter removed by subjecting the wastewater to a secondary treatment. Non-biodegradable components are removed from the wastewater during tertiary treatment thereof. The closed-loop treatment system produces a high quality water comparable to, or in many cases better than, commercially available potable water.

Description

CLOSED-LOOP WASTEWATER TREATMENT SYSTEM

BACKGROUND OF THE INVENTION

1. Field Of The Invention

This invention relates to wastewater treatment systems; and more particularly to a system for removing BOD₅ and TSS from discharge wastewater such as raw or untreated industrial process water, contaminated storm water or contaminated groundwater.

2. Description Of The Prior Art

Increased consumption of water for industrial applications has caused the water quality to deteriorate in many locations. Water shortages have emerged and the cost of water management has risen. The increased water usage has created pressure on municipal authorities to upgrade or expand their plants to meet current demand. Plant expansions have, in turn, increased costs of buying water, as well as costs associated with the discharge of wastewater and payment of surcharges.

SUMMARY OF THE INVENTION

The present invention provides a closed-loop wastewater treatment system that virtually eliminates the need for purchase of water from municipalities as well as the necessity for discharge of water to the municipalities. Regulations heretofore applicable to facilities which discharge wastewater are avoided and BOD₅, TSS and other surcharges are eliminated. Water of high quality is consistently produced and the cost of water is reduced.

Generally stated, the system provides for wastewater such as raw or untreated industrial process water, contaminated storm water or contaminated groundwater to be passed through a series of treatment processes until a desired quality is achieved. The wastewater treatment process comprises the steps of primary treatment, secondary or biological treatment and tertiary treatment, which are described hereinafter in connection with their application in the treatment system. BRIEF DESCRIPTION OF THE DRAWING

The invention will be more fully understood and further advantages will become apparent when reference is had to the following detailed description and the accompanying drawing, in which

Fig 1 is a process flow diagram of a closed loop wastewater treatment system utilizing primary treatment, secondary or biological treatment and tertiary treatment steps

DESCRIPTION OF THE PREFERRED EMBODIMENTS Referring to drawing Fig 1, primary treatment is carried out in Rotoshear 10 A screening system is designed to separate coarse (greater than 0 02 inch particle size) solids from the process This process is used to overcome plugging problems and minimize maintenance related work

Once large particulate matter is removed, the water is transferred to an equalization system 12 The equalization system 12 is designed to overcome the operational problems caused by variations in influent flow rate, concentration and pH

Wastewater from equalization system 12 is transferred to primary settling or floating tank P-DAF 14 for clarification or dissolved air flotation treatment During this treatment step, total suspended solids (TSS), heavy metals and other inorganic compounds found in many types of wastewater are removed Polymers are added to aid solids settling or floating, and facilitate solids removal

Once inorganic components of the wastewater are removed, the fluids are subjected to a secondary or biological treatment An immobilized cell bioreactor (ICB) 16 removes dissolved organic matter found in the wastewater The ICB is a fixed-film biological system designed for high efficiency in the removal of the dissolved organic matter In addition, ICB provides significant advantages in operation BOD5 and priority pollutants are removed ICB generates less biological solids than other biological processes, ultimately reducing sludge disposal costs The ICB system is physically compact, and can be custom designed to fit in small footprints ICB is an easier system to use, more reliable in operation and less expensive to maintain than other biological treatment systems

During residence in the ICB system, the microorganisms, in the presence of air, metabolize biodegradable compounds (BOD) into carbon dioxide (CO₂), water, new microorganisms and energy Nutrients such as phosphate and ammonia are added to augment biological activity and growth

Fluids from the ICB are transferred to secondary claπfier or dissolved air flotation chamber 18 Biological solids produced by conversion of BOD₅ using microorganisms in the ICB system are removed from the wastewater stream by DAF/claπfier 18 Bio-solids removal minimizes odor and algae growth in tanks and piping systems in contact with the wastewater The DAF/claπfier 18 utilizes rapid mixing, flocculation, chemical control and application Polymers are added to aid solids settling and removal

Fluids from DAF/claπfier 18 are transferred to vessel 20 for tertiary treatment Duπng tertiary treatment no biodegradable components of wastewater are removed The system design entails either a single process or a series of processes to achieve final design requirements In most cases, activated carbon is used to remove color and hard to remove organic material from the wastewater The system design includes a reverse osmosis (RO

22) system to remove chloride and/or total dissolved solids (TDS) The application of the closed-loop treatment system is especially suited to produce a high quality water comparable to, or in many cases better than, commercially available potable water

The following examples are presented to provide a more complete understanding of the invention The specific techniques, conditions, materials, proportions and reported data set forth to illustrate the principles and practice of the invention are exemplary and should not be construed as limiting the scope of the invention

Example 1

A closed-loop water recycling pilot system was installed at a textile finishing plant that utilized the "stone washing" process of blue jeans and other clothing This process is illustrated in Fig 2 Water from the laundry washers 1 flows to a catch basin 2 from which it is pumped to a shaker screen 3 where gross solids such as strings and fiber are removed The partially clarified water flows to a Equalization tank 4 Water from the equalization tank flows into a combined lamella claπfier/ primary Dissolved Air Flotation (DAF) system 5 that removes the suspended solids and fine fibers The clarified watei then flows into an

Immobilized Cell Bioreactor or ICB 6 where soluble organic compounds are removed by biological degradation The effluent from the ICB flows into a secondary DAF system 7 that removes the suspended biological solids The water from the secondary DAF flows into a clean water holding tank 8 that acts as a water reservoir for the laundry washers 1

Three factors which prevent the reuse of washing water for further washes are 1) suspended solids (measured as mg/L of TSS) which act to stain the washed jeans, 2) soluble organic compounds (measured as mg/L of BOD and COD) which interferes with the bleaching process and 3) hardness (measured in mg L) which leads to streaking of the washed and bleached jeans The effect of the treatment process train on these parameters is shown in table 1

Table 1 Removal of soluble organic compounds (COD/BOD), suspended solids (TSS) and hardness (mg/L) during treatment of wash water in a closed -loop water recycling system

BOD (mg/L) 400 400 <50 <30

TSS (mg/L) 1,000 <30 50 <5

Hardness 100-300 100-300 100-150 50-100

(mg L)

The wash water present in the catch basin contained a relatively high amount of soluble organic compounds (measured as COD and BOD) derived form soaps and detergents added to the wash and from starch which impregnates the jeans and other clothing It also contained stπngs and large pieces of fabric as well as dispersed fine fibers from the mechanical effects of washing The hardness of the water was about 300 mg/L The shaker screen acted to remove the larger pieces of fabπc but had little or no effect on soluble orgamcs and hardness nor even the fine, dispersed fiber (TSS) The fine TSS mateπal was reduced in the primary DAF from a level of about 1,000 mg/L to <30 mg/L There was little removal of either COD, BOD or Hardness in this step The ICB process was effective at removing soluble organic compounds but was also, effective at removing hardness Hardness is normally removed by ion exchange or RO membranes The effectiveness of the ICB system to remove hardness is an unexpected result of this process design for water recycling and enables the water to be recycled much more efficiently and cost effectively The final DAF system reduced residual biological solids and produced a water of high quality that could be reused in the washing process

The closed loop recycle system reduced COD in the washwater by >87%, BOD by >92%, TSS by >99% and hardness by 66% The unique combination of primary DAF, ICB biotreatment and secondary DAF treatment enabled washwater to be recycled without the use of expensive ion exchange or reverse osmosis membrane treatment

Example 2

The process of Example 1 was carried out and the build upon of salt was measured by mg/L of total dissolved solids (TDS) The results of this measurement are shown in Fig 3 After 9 recycles of the same batch of water the TDS had increased from only 1,500 mg/L to 4,500 mg/L The closed-loop water recycle system enabled the plant to use recycled water for washing textiles greater than 90% of the time without the use of a desalting membrane step The results shown in Fig 3 show that another limiting factor for the recycle of water for washing of textiles, namely, the build up of salt in the recycled water, was substantially eliminated by the ICB system Conventional biological treatment systems promote the active growth of bacteria to maintain a high level of bacterial activity This requires the addition of nitrogen and phosphate salts Furthermore, additional salts such as lime or ferrous sulfate are added as a flocculation and settling aid for removing excess biomass in the secondary clarification step The ICB system is a unique fixed film bioreactor technology that maintains biomass by entrapment rather than promoting bacterial growth This enables lower doses of nutrients to be used and the small amount of biomass produced can be removed in the secondary DAF by using organic polymers without the use of salt based settling agents As a result, the water can be recycled many times without the use of a membrane step for salt removal Example 3

A full scale closed loop water recycle system was installed at a commercial textile washing plant. This system is illustrated in Fig.4. The system consisted of a below ground catch tank, a rotoshear screen, an equalization and feed tank, a primary DAF system, an ICB vessel, a secondary DAF system, a catch tank and a clean water storage tank. This system recycled water from the plant's laundry washers at a rate of 100,000 gpd. This system was designed to treat washwater with a BOD of 700 mg/L, a TSS of 200 mg/L and a pH of 4-7 S.U. and produce a clean water for reuse containing a BOD of <30 mg/L, a TSS of <30 mg/L and a pH of 6-8 S.U. The closed loop water recycle system enabled the plant to use recycled water for >90% of the textile washings.

Having thus described the invention in rather full detail, it will be understood that such detail need not be strictly adhered to but that various changes and modifications may suggest themselves to one skilled in the art, all falling within the scope of the present invention as defined by the subjoined claims.

Claims

What is claimed is:

A system for treatment of wastewater, comprising the steps of

(a) subjecting such wastewater to a primary treatment to remove total suspended solids, heavy metals and inorganic compounds therefrom,

(b) subjecting said wastewater to a secondary treatment to remove biodegradable components therefrom, and

(c) subjecting said wastewater to a tertiary treatment to remove non- biodegradable components therefrom

2 A system for treatment of wastewater, as recited by claim 1, wherein said primary treatment step further comprises the steps of (i) screening said wastewater to separate coarse solids therefrom, (ii) equalizing said wastewater to overcome operational problems caused by influent flow rate, concentrations and pH variations, and

(iii) clarifying or treating said wastewater by dissolved air flotation to remove said solids, metals and inorganic compounds therefrom

A system for treatment of wastewater, as recited by claim 1, wherein said secondary treatment step further compπses the steps of

(i) contacting the wastewater with microorganisms in the presence of air to metabolize biodegradable compounds into carbon dioxide, water, new microorganisms and energy, and

(ii) treating said wastewater in a secondary clarifier or dissolved air flotation chamber to remove biological solids therefrom

A system for treatment of wastewater, as recited by claim 1 , wherein said tertiary treatment step further comprises the steps of

(i) contacting said wastewater with activated carbon to remove color and hard to remove organic material therefrom, and

(ii) subjecting said wastewater to a reverse osmosis system to remove chloride or total dissolved solids therefrom