LRWRP_Design_Report_Chapter_8.pdf

CHAPTER 8

SOLIDS HANDLING FACILITIES (TM 6)

Introduction

Assessing current conditions and future solids handling needs will form the basis of a sound solids handling facility design. Brown and Caldwell held a brainstorming meeting with the City of Lompoc Public Works Department Water Reclamation Plant management and staff on September 27,2004, to further d e h e concepts and criteria that would be a part of this solids handling facility design effort. A copy of minutes from this brainstorming meeting is included in Appendix A. An earlier brainstorming meeting was held to further define the concepts and criteria for the liquid process elements. Solids quantities and flow projections presented in this technical memorandum are based on selected liquid process elements discussed in the first brainstorming meeting.

The City's 2002 Master Plan for the LRWRP recommended the following improvements to the solids handling facilities:

Provide a second gravity thickener of equal size to the existing gravity thickener to improve redundancy.

Provide a third 76-ft diameter, 30-ft side water depth anaerobic digester to meet future solids loading and provide redundancy.

Provide permanent piping from the east lagoon to the drymg bed and h e and divide the lagoon into several compartments.

Provide a covered paved area for interim dried product storage and a paved area for further processing of dried product to make it more appealing for direct use by the public.

Brown and Caldwell reviewed these recommendations during preparation of our response to the RFP for this project. This technical memorandum provides details to address needed improvements in these four solids handling facihty process elements.

Objectives

As stated in the scope of work for this project and as discussed at the project kickoff meeting, the following objectives are addressed in this technical memorandum.

1. Evaluate solids handling recommendations and costs presented in the 2002 Master Plan.

Evaluate the impact of additional solids on thickener and digesters.

Evaluate existing solids thickening and different options for solids thickening.

Evaluate dissolved air flotation thickening versus gravity thickening.

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Solids Handling Facilities (IM 6) 8-2

Evaluate current solids handling system in light of its ability to produce Class A, Exceptional Quality biosolids on site.

Existing Conditions and Solids Projections

8.3.1 Existing Conditions

The existing solids processing facilities at the LRWRP were constructed in the early 1970s and consist of one gravity thickener, two anaerobic digesters, two sludge lagoons and one air drying bed.

A description of current solids processing equipment is included in Table 8.3-1.

Table 8.3-1. Existing Solids Processing ~acilitied")

Item

Gravity Thickener Number of units Tank diameter (ft) Sidewater depth (ft) Gross surface area (ft2) Effective surface area (ft2) Solids loading (lb/ ftz/day) Overflow rate (gpm/ ft2) Detention time, (hours) Thickened solids concentration (O/O)~

Anaerobic Digesters Number of units Tank diameter (ft) Side water depth Unit volume, each (gallons) Volatile solids reduction, design (O/o) Cover typed Mixing

Digested Sludge Lagoons Number of units Surface area, total (acres) Depth (ft) Gross storage volume ( d o n gallons)

Sludge Air Drying Beds Number of beds Drying bed area, (acres) Drying bed type

Value

28.5 507,575

Floating Pumped

Sand with underdrain

Information obtained from 2002 hlaster Plan unless noted otherwise.

b Effective surface area calculated by subtracting area occupied by effluent launder.

Thickened solids concentration reported in 2002 Master Plan.

d Surface area and depth obtained from existing plant design drawings design data sheet G3

Effective depth is somewhat less due to sludge accumulation

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Solids Handling Facilities P M 6) 8-3

I i 8.3.2 Solids Projections

The recommended liquid process will discontinue use of the existing primary clarifiers and trickling filter and use an oxidation ditch process for secondary treatment. Solids projections are made based on prehcted levels of treatment based on influent flow data obtained from the plant.

Five years of influent data have been evaluated to characterize projected influent wastewater strength. Table 8.3-2 summarizes solids projections for the recommended liquid process facilities based on these data. These solids projections assumed an influent cBOD of 338 mg/L with an oxidation ditch SRT of 10 days. Digested solids projections are shown for both 35 percent and 55 percent volatile solids reduction to demonstrate the potential impact of enhanced digestion using WAS disintegration. This technology is discussed in more detail below.

Table 8.3-2. Solids Projections

- 1 Average Daily I Peak Monthly Raw Solids TSS , lb/day VSS , lb/day Flow, mgda

TSS lb/day VSS lb/day Flow. m ~ d c, Digested Solids @ 35% VS reduction

Thickened Solids @ 5.0%

10,064 7,356 0.40

10,064 7,356 n n77 vss lb/day Flow, mgd

13,385 9,783 0.53

13,385 9,783 n nw o onn TSS lb/day

TSS lb/day a Flow from h a at 3,000 mg/L b Increased VSR from WAS disintegration technology

Additional 20% VS reduction in lagoons d Dredged solids concentration of 4.5%

7,500 4,800 0.027

~ p~ -

Flow, mgd

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6,400 0.032

6,000

0.027 I 0.032

February 2005

8,000

4.400 VSS Ih/dav

Lagoon solids to air drying - from 35% VS reduction

3.300

NA

Nil

NA

TSS lb/day VSS lb/day Flow, mgdd

6,500 3,800 0.017

Lagoon solids to air drying - from 55% VS reduction

NA

NA

NA

TSS lb/day VSS lb/day Flow, mgdd

5,400 2,600 0.014

Solids Handling Facilities (I'M 6) 8-4

8.4 Sludge Thickening

8.4.1 Evaluation of Existing Gravity Thickening vs. DAF Thickening

The existing thickening system thickens primary solids and waste activated sludge using a gravity sludge thickener (GST) described in Table 8.3-1. Review of process data provided in the 2002 Master Plan indicated that the GST was only achieving a thickened solids concentration of approximately 3.7 percent. This is consistent with experience at other similar treatment plants around the country. Because of the lower solids concentration the Master Plan also recommended addition of another digester. In response to the RFP, Brown and Caldwell recommended replacing the existing gravity thickener with DAFTs to increase thickened solids concentration and eliminate the need for another digester.

8.4.1.1 Gravity Thickening. Solids thickening in a GST is accomplished by gravity-induced settling and compaction. Gravity thickeners are used most successfully for thickening primary sludge, and to a lesser degree, combined primary and secondary sludge due to the differing particle sizes and density. Primary sludge would tend to settle more rapidly than the lighter secondary sludge particles. Since the new liquid process at LRWRP will discontinue use of the primary clarifiers, we would expect the performance of the GST to be reduced even further due to the absence of primary sludge. The GST would need to be re-rated for the new solids condition for a lower solids loading rate. Typical solids loading rates for a WAS only GST is about half of that used for combined solids thickening. Therefore, the existing GST would have half the capacity it currently has. To handle projected peak solids loading, with all units in service would require four 55 ft diameter GSTs. In addition, GSTs would have the effect of solubilizing the easily reduced organic solids, thereby increasing the BOD in the thickener overflow. Therefore, because the GST system would need to be expanded and the existing thickening facilities are approximately 30 years old and reachmg the end of their useful life, Brown and Caldwell doesn't recommend the use of GSTs for sludge thickening. No costs for expansion of the GST system are provided in this technical memorandum.

8.4.1.2 Dissolved Air Flotation Thickening (DAFT). As discussed in the brainstorming session and as noted above, the recommended thickening system will use DAFTs. DAFTs have been used for years to thicken WAS, primarily because this sludge is very light, settles with difficulty, and almost always comes at concentrations less than 10,000 mg/l. DAFTs do well on WAS because they efficiently float light material, can deal with solids that do settle, and can accept concentrations with large quantities of water whde still producing a relatively concentrated product with a high capture rate.

DAFTs produce thickened solids by floating solids to the surface rather than settling. This is accomplished by saturating a pressurized liquid with air combined with the feed solids to increase their buoyancy. When the air saturated pressurized liquid is depressurized to essentially atmospheric conditions, it produces fine bubbles (much hke the fizz that occurs when opening a soda bottle) that adhere to solids floc. This reduces the floc's specific gravity to less than 1.0 causing the floc to float.

As the float layer forms on the surface, liquid stdl contained in the floating solids drains out by gravity which causes further solids concentration to occur. The floating solids are slowly skimmed off the surface into a float collection box to be pumped to the digesters. Heavier organic solids and gnt settle to the bottom and can be removed as bottom sludge. A simplified schematic of a DAFT is shown in Figure 8.4.1.

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Solids Handling Facilities (TM 6) 8-5 turation Tank DAF Thickener

Feed Sludge

Figure 8.4.1. Dissolved Air Flotation Thickener Schematic1

1. "State-of-Practice of DAFT Technology - Is There Still a Place For It," Bratby, J; Jones, G.; Uhte, W, WEFTEC 2004 proceedings, October, 2004

Key components of the DAFT include the saturation system, air compressor, level control system, and polymer feed system. An important operating parameter that needs to be controlled is the air to solids ratio. Adjusting the air to solids ratio does not increase the concentration directly, but it does contribute to the depth of the float layer at the surface. Because this facility wlll be wasting mixed liquor continuously, the solids loading rate should be fairly steady so the air flow rate may only need periodic adjustment. A variable speed dnve andlor timer will be included to control the skimming arm speed to control the solids removal rate. A minimum of two float hoppers will be provided to reduce the distance float is moved on the surface resulting in less disturbance to the lower levels of the float. Some of these parameters can be automated through process monitoring instxwnentation and controls to reduce operator attention.

The new DAFTs will be constructed in the area currently occupied by the remains of Trickling Filter 1. Since the superstructure, filter media and internal mechanisms have already been removed, demolition work only includes concrete demolition of the lower plenum portion of the old trickling filter. All equipment, with the exception of air compressor equipment, will be mounted in a free-standing steel canopy structure rather than being housed in a building to save on the expense of a building. Air compressor equipment may be housed in a weather-proof, sound-insulated enclosure.

The design of the DAFTs for this project will include a polymer feed system that may be used to improve performance during peak solids conditions when sludge wasting is highest. No permanent polymer storage tanks will be provided because the limited amount of polymer that may be needed can be purchased in recyclable portable totes. Polymer pumps and a storage area for the portable totes will be within a containment area to control spds. Dual pressurization and sludge pumps will be provided for redundancy and operator flexibihty. Positive displacement rotaly lobe or progressive cavity pumps will be used to pump the thickened sludge to the hgesters. Pump selection will be further evaluated during detailed design.

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Solids Handling Facilities (TM 6) 8-6

To control odors, the DAFTs wdl be covered with flat covers. Foul air will be withdrawn at a sufficient rate to maintain a negative presswe below the covers. A typical DAFT with low profile covers is shown in Figure 8.4.2. The method of foul air treatment will be h t h e r evaluated during detailed design. Design criteria for the DAFTs are summarized in Table 8.4-1. Following the brainstorming meeting the City requested having a waste grease receiving station provided on site to facilitate lawful waste grease disposal for grease collected from restaurants. Since grease naturally floats, combining the grease with raw solids being fed to the DAFTs would be the logical place to locate this grease receiving station. Grease hauler waste is assumed to be free of larger rocks, etc, so pretreating the grease waste is considered unnecessary. The grease receiving station will include a bermed area where grease haulers dump their waste through a quick connecting fitting they can hook up their discharge hose to. A plant water hose station will be provided for cleanup.

Table 8.4-1. Dissolved Air Flotation Thickening Design Criteria

Float solids concentration (without polymer addition at average flow)' I

Parameter Numbera

Diameter (ft)

Effective surface area (ft2)

Solids loading (Ib/ ft2/day)b

Saturation system pressure (pig)

Value

1,200

15-1 8

Saturation system capacity (scfm)

Pressurization pump capacity (gpm)

Air to solids ratio

Float collection arm speed (RPH) Float pumps, No. each DAFT

Includkg 25% bottom sludge recycle Performance based on experience from other similar facilities. Polymer would be needed during peak loading conditions.

Float pump capacity, gpm

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100-1 50

February 2005 a Number of units assumes one unit out of service during average conditions.

Solids Handlmg Facilities (TM 6) 8-7

Figure 8.4.2. Typical D U T s with Low Profile Covers

8.5 Solids Digestion

During the solids handhg brainstorming meeting, anaerobic and aerobic digestion processes were discussed. Brown and Caldwell stated it knows of no facilities that discharge aerobically digested sludge into lagoons and believed that odors from the lagoon would be higher than lagoons receiving anaerobically digested sludge. Following the meeting, the City decided that no further evaluation of aerobic digestion was warranted. As noted in the meeting minutes, the City identified several improvements they would like to see done to the existing anaerobic digesters such as replacing mixing pumps with chopper-type pumps and replacing corroded piping. Another suggested improvement included replacing the floating covers with fixed covers. The City has decided to proceed with these improvements using City staff. No modifications to the existing digesters will be included in Brown and Caldwell's design. No costs are provided in this technical memorandum for any modifications to the digesters that may be necessary.

The existing facilities include two anaerobic digesters. The 2002 Master Plan recommended that a third %ester be built to handle increased solids loading based on a thickened solids concentration of approximately 3.7 percent from the gravity thickening system. By replacing the existing gravity thickening system with DAFTs, the thickened solids concentration will be increased, making

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Solids Handhg Facilities VM 6) 8-8 construction of a third digester unnecessary. Since the new liquid process will be feeding thickened WAS only to the dgesters, the volatile solids reduction is expected to be below the 38 percent required to meet vector attraction requirements of the EPA 40 CFR 503 regulations. As such, it is important that additional stabilization take place in the lagoons that follow the anaerobic dgesters.

8.5.1 WAS Disintegration

New technologies have been in operation in Europe for several years that are being used to improve the dgestion process. These technologies use various disintegration methods to break down the floc and cell structure of WAS solids, releasing nutrients and enzymes that can be more easily digested. The ultrasound process uses energy transmitted to the liquid stream through high frequency transmitters. The transmitters convert electrical energy into ultrasound waves that create cavitation (rnicrobubbles) in the liquid stream. As the microbubbles form and collapse, extreme high pressure and temperature are released inside the bubbles. The resulting pressure waves disrupt the weak cell structure of the WAS solids releasing water contained in the organisms and changing the particle size and particle charge distribution.

Brown and Caldwell has been evaluating WAS disintegration technologies for the past two to three years. Brown and Caldwell visited a facility in Mannheim, Germany, in September, 2003 that was using this technology on a portion of their thickened sludge flow to the anaerobic digesters. The ultrasound disintegration system had been in operation for about 1 $5 years when the visit was made.

Since the system had been in operation, the plant has seen an increase of about 20 percent in the gas production from their digesters as well as a reduction of the volattle solids content in their digested sludge from 54 to 50 percent. Specific VSR values were not available. Insufficient detail was available to determine how much of this improvement could be attributed to the ultrasonic system.

Recent research done by the Orange County Sanitation District on a similar ultrasonic system to improve volatile solids destruction for WAS digestion has shown s d a r results. The City of Riverside is also conducting pilot testing of this system to verify whether this system would be a cost effective improvement to their digestion system to produce more gas that can be used in their cogeneration facility. T h s pilot test has only been in operation for about a month, so limited data are available to show how the system is operating. As shown in Table 8.3-2, increasing the VSR in digestion w d have a dramatic effect on the volatile solids loadmg in the lagoons as well as reducing the amount of solids that will need to be hauled away. The impact of improved VSR on lagoon sizing is shown below. Brown and Caldwell recommends proceeding with testing of this technology once the current round of research and testing are completed at various locations around the US and Europe and data collected in the 2005/2006 timeframe. Implementation of this technology could occur by 2008 to 2010 as a part of Stage 2 improvements.

8.5.2 Digestion Process Issues

At the brainstorming meeting, the City described operation of the drgesters as a series primary and secondary digestion system. Thckened sludge is fed to the primary dgester, whch causes an overflow to the secondary drgester. Both the primary and secondary digesters are heated and mixed.

The required volume to provide a minimum hydraulic detention time of 15 days at peak flow with both units in service and 18 days at average flow with one unit in service, can be met by one of the two existing digesters at the anticipated thickened solids concentration. When the primary digester

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Solids Handling Facilities (TM 6) 8-9 is out of service for cleaning, the secondary digester would need to act as the primary dtgester.

Future addition of tertiary treatment processes for metals removal are expected to produce a minimal amount of additional sludge. The volume of this additional sludge may reduce the hydraulic detention time slightly. Since the digested sludge will be further stabilized in the lagoon system this reduced detention time is considered to be insignificant.

The City also explained that digested sludge is being sent to the lagoons from the secondary digester by gravity. Dilution water is added to the digested sludge to help it flow by gravity to the lagoons and prevent solids from settling in the pipe. After the new thickening system is placed in service, the digested sludge concentration will increase due to the thicker feed sludge. Therefore, more dilution water would be needed to assist flow of this digested sludge to the lagoons by gravity.

Dilution water would increase the flow going to the lagoons and may adversely affect solids settleability in the lagoons. Instead, Brown and Caldwell recommends adding a digested sludge transfer pumping system using non-clog centrifugal pumps to pump sludge to the lagoons rather than use the gravity sewer system. Pump selection will be evaluated in more detail during the design phase of the project. The cost of the transfer pumping system is included in the improvements needed for the lagoons.

8.6 Sludge Lagoons

8.6.1 Class A Biosolids Issues

The sludge lagoons play an important role in the solids handling system. Facultative lagoons provide the additional sludge stabilization needed to provide sufficient volatile solids reduction to meet the requirements of the EPA 40 CFR 503 regulations (503 regulations) for vector attraction reduction (VAR). The recently completed Water Environment Research Federation PERF) study on low technology methods of achieving Class A biosolids suggests that if sufficient pure storage time is provided in a lagoon (one to two years), the lagoon could produce Class A biosolids under the requirements of the 503 regulations for Alternative 4. Testing of the fmal disposal product would be required to verify sufficient pathogen reduction to meet Class A requirements.

Review of the solids projections shown in Table 8.3-2 indicates that the existing lagoon volume is insufficient to provide the necessary "pure storage" time to achieve the required pathogen reduction for Class A biosolids. Therefore, additional lagoon space would be required. However, since the City sends their dried biosolids to a composting facdity, the City currently does not need to produce Class A biosolids on site. Nevertheless, the City wants to have the flexibility to produce Class A biosolids on site.

There are two approaches for achieving Class A biosolids on-site. These approaches could be implemented in two stages. The &st approach would be to utilize both existing lagoons, feed both lagoons, and dredge from them as necessary to the drying bed. There is no "pure storage" operational mode here and, as noted in the Biosolids Management Plan, some pathogenic organism may still exist in the solids leaving the lagoons to air drying. Under this approach, Class A biosolids would be achieved by drying to an extremely high solids content on the drying bed, to provide necessary pathogen destruction via dessication. Research has shown that probably 95 percent solids

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Solids Handling Facilities (TM 6) 8-1 0 would be required for this approach to be successful. We would recommend that the City plan for 95 percent solids before removing material from the drying bed, p h g the material up, samphg the pile and analyzing samples for Class A pathogen densities.

The second approach for acheving Class A biosolids on-site, would be to expand the lagoon system to four lagoons to acheve a minimum of one year "pure storage" of all material w i t h the lagoon before going to the drying bed. Thls approach would achieve Class A material within the lagoon, and the drying bed would be used only to dry the product to perhaps 70 to 80 percent solids to make it easier to handle and to reduce hauling costs. The length of "pure storage" time is only an estimate. Research shows that one year may be margmal in achieving Class A material. Based on experience at the Sacramento Regional plant, two years "pure storage" time has been successful in achieving sufficient pathogen destruction on a consistent basis. Due to site lirmtations, providing two years of "pure storage" time is not feasible. The final dried product would stiU need to be piled up, sampled and tested, and await the results before the pile could be declared to be Class A material.

Due to the samphg/analytical requirements for both Class A approaches, we would suggest that one "annual" pile be created under either option. Since sampling and analysis takes several months, the annual pile should be created in the fall and sampling and analysis should be performed over the winter. If the pile passes the Class A test, it can be disposed of as a Class A product in the spring of the following year.

8.6.2 Lagoon Improvements

The City described a fill and draw mode of operation for their sludge lagoons. Sludge is drawn from the lagoon using a portable "Pit Hog" pump, and pumped to the sludge drying bed on the opposite side of the plant through temporary piping. The City indcated they are only able to pump out the top few feet of the sludge layer in the lagoon because their suction piping wdl not reach the bottom and the sludge becomes too thck to pump the deeper they go. Therefore, the active volume of the lagoon has decreased from the original design. To restore this volume to original design conditions, the solids will need to be dredged out of the lagoon. The City can do t h s in preparation for other modfications recommended in the Biosolids Master Plan before construction begins on the new facilities. Improvements to the lagoons can be accomplished in two stages.

8.6.2.1 Stage 1 Improvements. The Biosolids Master Plan recommended that one of the lagoons be lined with an asphalt liner with concrete paved slopes and concrete divider walls to prevent mixing sludge being added to the lagoon with the sludge already stored, and convert the other lagoon to an alternate use. It also recommended that permanent piping be installed from the lagoon to the drying bed area using 6" PVC or HDPE pipe. Review of solids projections in Table 8.3-2 indcate that the volatile solids loadmg with only one lagoon in service would be in excess of 60 lb/day/1000 ftz, which could produce a significant amount of odor. Therefore, Brown and Caldwell recommends that both lagoons be h e d and remain in service. To reduce construction costs, we also recommend that a soil/bentonite clay liner be installed in the bottom and up to half the depth of the lagoon and the remaining (i.e., upper) side slopes be lined with a hypalon h e r instead of the asphalt and concrete h e r recommended above. This type of liner has been used successfully in Goleta for over 15 years. With two lagoons in service, it will no longer be necessary to compartmentalize one lagoon, thus eluninating the need to construct a costly concrete partition wall.

February 2005

Solids Handling Facilities (TM 6) 8-1 1

The levees surrounding the existing lagoons will be raised by 3 feet or the bottom dredged to increase the depth of the lagoons to 15 feet. The method used to increase the depth of the lagoons will be determined after evaluating the soil stability and the water table level.

To provide more efficient solids removal, a floating dredge with an adjustable suction boom is also recommended. The discharge from the dredge would be tied to the permanent piping along the shoreline by a floating flexible hose. Although the floating dredge will be equipped with its own pump, a booster pump also may be needed to provide sufficient head to pump the dredged material to the drying bed. A surface paddIe mixer will be provided in each lagoon to keepthe surface layer aerobic and prevent scum mats from accumulating. These two items were not included in the 2002 Master Plan and will add to the cost of the lagoon upgrades; however, some of this added cost should be off-set by using a less expensive lining system. Some secondary effluent water will be added to the surface of the lagoons to maintain a minimum liquid depth to make up for natural evaporation and to reduce odors. New or modified supernatant overflow structures will be provided in the two lagoons with flow being routed to the head of the oxidation ditches.

8.6.2.2 Stage 2 Improvements. To provide a minimum of one year "pure storage" time to achieve Class A pathogen reduction before air drying, it would be necessary to construct two more lagoons.

The lagoons would be operated with two lagoons being filled, one in storage and one being dredged.

Dredging would take place in the spring following the end of the rainy season to allow the solids sufficient time to air dry. This would allow an additional 6 months of storage during the colder winter months for additional stabilization. Design criteria for the Stage 2 sludge lagoons are summarized in Table 8.6-1.

As shown in Table 8.6-1, achieving a higher VSR from digestion will sipficantly reduce the additional surface area required for lagoons or allow a lower VS loading rate for reduced odor production and better solids separation. The governing factor which determines the number of lagoons required is the one year minimum "pure storage" volume required. To provide the necessary number of lagoons for fill, storage and dredging, two additional lagoons would be needed.

One lagoon could be constructed on the southwest side of the site adjacent to the new oxidation ditches, and the other lagoon could be constructed on the north side of the EHD.

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Solids Handling Facilities ('I'M 6) 8-12

Table 8.6-1. Stage 2 Sludge Lagoon Design Criteria (To Achieve Class A in Lagoons)

Sludge Air Drying Bed and Dried Product Storage

Parameter

Sludge is periodically removed from the lagoons and pumped to a single discharge point at the west side of the sand drying bed during the drying season (April - November) when the dry pan evaporation rate is the highest. Liquid drains from the sludge through the sand layer and into the collection pipes and is returned to the head of the plant for recycle stream treatment. The solids that remain on the surface are allowed to air dry to approximately 90+ percent. Once the material is sufficiently dry, the dried material is scrapped off the surface by a private contractor and stored in an open area on the north side of the drying bed. As the dried solids are being removed, some of the top sand layer is also removed. The sand layer may need to be restored from time to time.

Value

8.7.1 Drying Bed and Product Storage Improvements

The improvements described below may be implemented in two stages.

Digested WAS from Oxidation Ditch Process

8.7.1.1 Stage 1 Improvements. The Biosolids Master Plan recommended that 1.25 acres of the interim storage area be paved and that 5,000 ft2 of it be covered to prevent rain from rewetting the dried material and make to loading operations easier. The paved area will be designed per City paving standards for moderate traffic loading, and an open sided pre-engineered canopy stmcture will be placed over part of the paved storage area. Design of the paved storage area will be refmed once actual soil conditions are known.

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Digested sludge @ 55% VSRa

30b

2.5

0.5

Volatile solids loading, lb/d/1000 ft2 Pure storage time required, years (min) Surface area required, acres Available surface area, acres Additional surface area required, acres Digested sludge flow, MG/yr Volume required, MG Available volume, MGc Additional volume required, MG Additional volume provided, MGJ Number of additional lagoonsd

February 2005 a Increased VSR from WAS disintegration technology Lower VS loading allowed due to higher VS reduction in digesters Liquid depth increased to 15 ft by raising levees or bottom excavation d Additional volume and number provided to allow fa, storage and dredging mode of operation and match existing lagoon volume for ease of operation

Digested sludge

@ 35% VSR

2.7

0.7

Solids Handling Facilities V M 6) 8-13

8.7.1.2 Stage 2 Improvements. To eliminate periodic replacement of sand removed when dried solids are removed from the drying bed, and to facilitate faster drying, the City may elect to pave a portion of the existing sand drying beds. The paved area would facilitate the use of mechanical rubber-tired equipment that could turn the sludge over during the drying process to expose more surface area to the air and thus accelerate the drying process and promote a smaller dried product particle size. The drying process would take place through evaporation rather than draining to a subsurface drainage system. Based on a solids loading rate of 15 lb ~ ~ S / f t ~ / ~ e a r , approximately two acres would need to be converted to a paved drying bed. To construct the paved drying bed, the top sand layer could be compacted to approximately 95 percent and paved over with asphalt. Pavement will be designed to meet City paving standards. Final pavement design will be refined when actual soil conditions are known. Perimeter drainage ditches would be provided to keep surface run-off from inundating the material as it is drying. Because the drying bed area is in a depressed area similar to the lagoons, it could be used as a storm water holding pond during the wet season when drying operations are not being conducted. The benefits of paving the drying bed area would include: quicker drymg time due to turning material as it dries, better product quality without sand, reduced bed maintenance by elimination of sand layer replacement, and removal of drying bed underdrain recycle flow to the headworks.

Recommendations

Recommendations for solids handling improvements are described below. Table 8.8-1 summarizes -- pertinent design criteria described earlier. These recommendations may be implemented in two stages to facilitate phased funding requirements.

8.8-1 Stage 1 Improvements (To Be Included in Lompoc RWRP Upgrade Project)

Thickening:

Two - 40 ft diameter DAFTS with ancillary equipment, thickened sludge pumps and odor control

Grease interceptor waste receiving station

Lagoons:

Two lagoon feed pumps located at existing digesters

Line both lagoons with bentonite/soil and hypalon liner

Two floating paddle mixers

New supernatant return structures in each lagoon

One sludge dredge with adjustable boom

One booster pump station for feed to drying beds

Raise levees 3 feet or excavate bottom of lagoon 3 feet to provide 15 ft liquid depth and additional storage volume

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Solids Handling Facilities (TN 6) 8-14

Install permanent 6 inch PVC piping from lagoons to drying bed

Air Drying Beds and Dried Product Storage:

Pave 1.25 acre storage area with 8 inch gravel base and 4 inch asphalt topping 5,000 ft2 open sided canopy covered storage building

8.8.2 Stage 2 Improvements (Optional Items)

Thickening:

Rotary drum raw sludge screen

Test WAS disintegration system - install permanent system if test is successful

Lagoons (for Class A biosolids before air drying)

Construct two additional lined lagoons with paddle mixers and supernatant structures and piping to connect to air drymg.

Air Drying Beds

Pave 2 acres of existing sand drying beds with 3 inch asphalt pavement over re-compacted sand and gravel base.

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Solids Handling Facilities 6) 8-15

Table 8.8-1. Solids Handling Facilities Design Criteria Summary

Parameter a Increased VSR from WAS disintegration technology b Lower VS loading allowed due to higher VS reduction in digesters

Liquid depth increased to 15 ft by raising levees or bottom excavation Additional volume and number provided to allow fa, storage and dredging mode of operation and match existing lagoon volume for ease of operation

Value addtion at average flow)^ Saturation system pressure (psig) Saturation system capacity (scfm) Pressurization pump capacity (gpm) Xir to solids ratio Float collection arm speed (RPH) Float pumps, No. each DAFT Float pump capacity, gpm

P:\-Projects\l26517 - LOhlPOC\\XT\Project-Report\IO33979 Preliminary D e s p Report Find.doc

5.0

0.03 - 0.04

0.38 - 1.14

100-150

February 2005

DAF Thickening N u m b e ~ Diameter (ft) Effective surface area (ft2)

Solids loading (lb/ ft2.d)" Float solids concentration (without polymer a Number of units assumes one unit out of service during average conditions.

b Including 25% bottom sludge recycle

Performance based on experience from other similar facilities. Polymer would be needed during peak loading conditions.

Stage 2 Lagoon Improvements to Achieve Class A

1,200 15-18

5.0 - 5.5

Digested sludge @ 55% VSRa

30b

2.5

0.5

Volatile solids loading, lb/d/1000 ft2 Pure storage time required, years (rnin.)

Surface area required, acres Available surface area, acres Additional surface area required, acres Digested sludge flow, MG/yr Volume required, MG Available volume, MGc Additional volume required, MG Additional volume provided, MGd Number of additional lagoonsd

Digested sludge

@ 35% VSR

2.7

.0.7

Solids Handling Facilities (I'M 6) 8-1 6

Preliminary Cost Estimate

8.9.1 Stage 1 Improvements

The preluninary estimate of probable construction cost for the Stage 1 improvements described above is $5,271,000 as indicated for TM 06 in Table 2.1-2. A detailed breakdown of this estimate is provided in Appendix B.

This estimate includes costs for items that were not included in the 2002 Master Plan. These items include:

Lining of the second sludge lagoon needed for adequate volatile solids loading. Cost savings for second lagoon may be expected by using bentonite/soil liner rather than asphalt and elimination of freestanding concrete divider walls. Depending on soil conditions and thickness of clay liner, costs may be somewhat higher than shown.

Cost for lining both lagoons is based on a 6-inch bentonite/soil liner.

Dredge for efficient removal of sludge from lagoons.

Lagoon surface paddle mixers to keep surface aerated and reduce scum accumulation that could cause odors.

8.9.2 Stage 2 Improvements

Construction costs have been estimated for the recommended Stage 1 improvements and Stage 2 I lagoon improvements described above. Estimated costs are based on recent similar construction projects on the west coast where available or the latest edition of Mean's Construction data.

Table 8.9-1 summarizes these capital costs. Detailed cost estimates are included as an attachment.

Table 8.9-1. Summary of Estimated Construction Costs for Stage 2 Solids Improvements

I tem Sludge Lagoon Improvements Sludge Air Drying/Storage Improvements

Subtotal

Cost ($1,000)

81 1

Contractor Mark-up, 16% Contractor General Conditions, 8%

Sales Tax, 8%

Subtotal 1 1,281

Performance and Payment Bonds, 2% Builders Risk & Liabihty Insurance, 2%

This cost estimate does not include the following:

Contingencies, 25% Total Construction Cost

1. Potential thickening improvements

2. Escalation to the rnid-point of construction

3. Startup, training and 0&hI

1,601

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