- Supplementing the water supply, eliminating the need

Testing In-Line Filtration for Reclamation of Pure Oxygen Activated Sludge Secondary Effluent Domgnec Jolis, Process Engineer Rochelle Campana, Assist...
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Testing In-Line Filtration for Reclamation of Pure Oxygen Activated Sludge Secondary Effluent Domgnec Jolis, Process Engineer Rochelle Campana, Assistant Civil Engineer Ashley Muller, Process Engineer Paul Pitt, Sanitary Engineer Bureau (of Engineering, Department of Public Works, City and County of San Francisco, CA 94124 Water reuse has been commonplace throughout history, specially in arid climates. Although treated wastewater has been used for field and crop irrigation in California for some time, in recent years, due in part to a long drought period, this practice has become more widespread. Reclaimed wastewater is now used extensively for the irrigation of parks and golf courses, groundwater recharge, and process water in industrial applications. Many benefits have been identified - Supplementing the water supply, to develop additional supplies - Reliabili.ty and less dependency - Avoiding capital and operating disposal facilities

with water reusel: eliminating the need on weather costs of wastewater

With these or similar benefits in mind, the City and County of San Francisco mandated in 1991 maximum utilization of reclaimed water as a means of augmenting its water supply. A Master Plan is currently being developed which will implement a Water Reclamation Program. Potential users of 20.5 mgd (77,556 m3/d) of reclaimed water have been identified. Almost all of these users require reclaimed water which meets full Title 22 regulations2 . Existina wastewater treatment facilities The City and County of San Francisco currently operates and maintains three wastewater treatment plants: North Point, Southeast, and Oceanside Water Pollution Control Plants, referred t o as NPWPCP, SEWPCP, and OSWPCP, respectively. The first two plants treat all the flow from the Ba,yside of the City. NPWPCP, which provides only primary treatment, is only used for treating wet weather flows in excess of SEWPCP capacity. At the time the work described in this paper was performed, OSWPCP was under construction. It is now operational.

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SEWPCP a n d OSWPCP p r o v i d e s e c o n d a r y t r e a t m e n t of a l l d r y w e a t h e r f l o w s , and o p e r a t e under d i s c h a r g e p e r m i t s i s s u e d by t h e C a l i f o r n i a Regional Water Q u a l i t y C o n t r o l Board (RWQCB), San F r a n c i s c o Region i n conformance w i t h t h e N a t i o n a l P o l l u t i o n D i s c h a r g e E l i m i n a t i o n System (NPDES)

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SEWPCP p r o v i d e s s e c o n d a r y t r e a t m e n t f o r a d e s i g n a v e r a g e d a i l y f l o w o f 85.4 mgd (323,200 d / d ) w i t h a maximum d r y w e a t h e r c a p a c i t y o f 142 mgd (537,500 m3/d). P e a k h y d r a u l i c c a p a c i t y i s 210 mgd (795,000 m 3 / d ) . Analogous numbers f o r OSWPCP a r e a d e s i g n a v e r a g e d a i l y f l o w o f 2 1 mgd (79,500 m3/d), a maximum d r y w e a t h e r c a p a c i t y of 4 3 mgd (162,700 m3/d) and a peak h y d r a u l i c c a p a c i t y o f 65 mgd ( 2 4 6 , 0 0 0 m 3 / d ) . Secondary t r e a t m e n t i n b o t h p l a n t s i s accomplished w i t h pure-oxygen a c t i v a t e d sludge systems.

* .

* The W a s t e w a t e r Reclamation Criteria from the California A d m i n i s t r a t i v e Code, T i t l e 22, D i v i s i o n 4,, C h a p t e r 3, S e c t i o n 60301 t h r o u g h 60355 ( T i t l e 22) r e l a t e t o treatment of w a s t e w a t e r f o r various reclamation uses. F o r T i t l e 22 u n r e s t r i c t e d u s e , w a s t e w a t e r must b e filtered, and oxidized, coagulated, clarified, d i s i n f e c t e d t o a 7-day moving median c o l i f o r m c o u n t o f 2 . 2 p e r 1 0 0 m i l l i l i t e r s , and a 30-day maximum o f less t h a n 23 p e r 1 0 0 m i l l i l i t e r s . E f f l u e n t t u r b i d i t y can n o t e x c e e d a n a v e r a g e o f 2 t u r b i d i t y u n i t s and can n o t e x c e e d 5 t u r b i d i t y u n i t s more t h a n 5 p e r c e n t of t h e t i m e d u r i n g any 24-hour p e r i o d . The r a t i o n a l e b e h i n d T i t l e 22 t r e a t m e n t a n d water q u a l i t y c r i t e r i a i s t h a t of providing e f f e c t i v e v i r u s destruction t o p r o t e c t p u b l i c h e a l t h 2 a . T i t l e 22 i s c u r r e n t l y b e i n g r e v i s e d 2 b . A l l r e f e r e n c e s i n t h i s p a p e r are t o t h e 1978 A d m i n i s t r a t i v e Code, which w a s i n e f f e c t at: t h e t i m e o f t h e p i l o t study.

W

T i t l e 22 ( S e c t i o n s 60303-60306) r e q u i r e s f u l l t r e a t m e n t wastewater, i.e. r a p i d mix, fl.occulation, of c o a g u 1a t i o n , cl a r if ic a t ion , f i 1t r a t i o n , and d i s i n f e c t i o n t o permit t h e use of reclaimed water. T it le 22, S e c t i o n 60320.5 a l s o recognizes t h a t a l t e r n a t i v e t r e a t m e n t p r o c e s s e s may p r o v i d e a d e q u a t e t r e a t m e n t and r e l i a b i l i t y . T h i s i s t h e case w i t h I n l i n e F i l t r a t i o n where t h e c l a r i f i c a t j - o n s t e p i s e l i m i n a t e d and coagulant and f i l t e r a i d s are added upstream of t h e f i l t e r without a s e p a r a t e f l o c c u l a t i o n u n i t (See Figure 1). DOHS s t a n d a r d s f o r t e r t i a r y t r e a t m e n t p r o c e s s e s have been reviewed elsewhere3

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I n 1988, t h e DOHS p u b l i s h e d s p e c i f i c r e q u i r e m e n t s f o r p r o c e s s equipment and f e e d w a t e r q u a l i t y f o r w a s t e w a t e r reclamation p l a n t s t h a t used Direct F i l t r a t i o n 4 . A t t h e t i m e of t h i s s t u d y , t h e DOHS h a d n o t p u b l i s h e d

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criteria for In-line Filtration. The criteria for Direct Filtration were used as the basis of this pilot study. The! DOHS requires pilot testing to demonstrate equivalency in effectiveness and reliability before an alternative process is approved. Title 22 states that "once an alternative method of treatment is approved for a specific installation, it generally will be acceptable at other locations in the State". The approval of In-Line Filtration as an acceptable alternative t o full tertiary treatment will give the City of San Francisco increased flexibility in siting water reclamation plants. Because of its reduced area and equipment requirements, it will also make any water reclamation scheme more economical, increasing the chances for its success. The objectives of this study are: - To consistently meet Title 22 use requirements for irrigation, fire fighting and toilet flushing, using In-Line Filtration of pure-oxygen activated sludge secondary effluent - To generate operating data, which will substantiate the ability of In-Line Filtration to meet Title 22 use requirements, under dry and wet weather conditions - To evaluate filter performance, and treatment reliability under a range of influent conditions - To determine the optimum range of coagulant and polymer dosages under a range of influent turbidities Materiala and .Method6 . auipment d e s c w . The pilot filter used in this study was a MULTIWASH~ filter, a deep bed single media gravity filter with simultaneous air and water backwash. The total available filter area was 0.54 sqft (0.05 m2). Backwash storage was provided by a 90 gallon (0.346 m3; 1.5 backwash volumes) aluminum tank. The underdrain distributor was a media-retaining nozzle with an air wash tail pipe. Two manually-controlled chemical metering pumpst fed alum and polymer as needed. Polymer was pumped just ahead of the filter, whereas alum was fed through a half inch (1.77 cm) diameter static mixer into a garden hose, the length of which provided enough time for coagulation t o occur before the feed stream reached the filter media. F i g u r e 2 shows the pilot filter flow schematic. The filter media was 1.5 mm effective size anthracite with a uniformity coefficient of 1.7. The bed depth was 48" (1.22 m). A variable speed pump, capable of providing flowrates from 1 to 10 gpm (0.063 t o 0.631 l/s), served as both feed and backwash pump. The same piping was used in both filter and backwash modes, by

5 General F i l t e r Company, Ames, Iowa t Liquid Metronics, Inc.

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controlling the direction of flow with four automatic valves. Filter backwash was automatically initiated by high effluent turbidities, terminal headloss or time. Manual backwash initiation was also possible. Influent and effluent turbidity (NTU), headloss across the filter (inches), feed flowrate (gpm) and time of day were continuously monitored. A chlorine contact channel (CCC) was constructed of 216

ft. (65.84 m) of 6" (15.24 cm) diameter PVC pipe. Flow through the CCC was by gravity, driven by 5' (1.52 m) of static head available in the backwash storage tank. A final effluent weir ensured that the channel flowed full. Filter effluent was injected with sodium hypochlorite (0.2% w/w) downstream of the backwash storage tank, just upstream of the CCC. Chemical injection was controlled by a chemical metering pump. The hypochlorite solution was mixed using a 1.215'' (3.17 cm) diameter double-chamber static mixer. Tracer field tests (data not shown) demonstrated that. the static mixer provided excellent mixing and that plug flow characterized 80% of the hydraulic regime in the channel. Mean hydraulic residence time (MHRT) was 125 min. Two amperomet ric, gold/copper elect roe5e, on-line chlorine analyzers* were used to continuously monitor chlorine residuals at the beginning and end of the CCC. F i g u r e 1 is a flow schematic of the pilot filter. Feedwater characteristics. Feedwater to thle filter was pure-oxygen activated sludge secondary effluent pumped directly out of the SEWPCP secondary effluent channel, upstream of the chlorine diffuser. Table8 1 and 2 summarize feedwater characteristics during the length of the study. When turbidities corresponding to simulated high solids loading (HSL) are not considered, the average secondary effluent turbidity was 4.9 NTU, with a maximum value of 7.1 NTU. Based on daily values from 1/1/08 to 9/30/91 (data not shown) , the secondary effluent average turbidity at SEWPCP was reported to be 5.0 NTU with 7.1 NTU at the 0 7 % percentile. The influent turbidity values experienced throughout this study are therefore representative of normal conditions at the SEWPCP. Maximum 24-hour average turbidities were below 10 NTU, the upper limit for feedwater quality set by the DOHS for use with Direct Filtration.

+

Capital Controls Company, series 1870E

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Operating parameters and Data collection. Filtration rate was maintained at 5gpm/sqft (6.3~10-3m/s), the maximum allowed by the DOHS for Direct Filtration. Backwash cyc1.e duration was set at 9 minutes. It was initiated either automatically, at a terminal headloss across the bed of 76 inches, or manually. The first 6 minutes consisted of a simultaneous air-water 'multiwash' cycle, at a water flowrate of 12 gpm/sqft ( 1 . 5 1 ~ 1 0 -m/s)and ~ an air flowrate of 3 cfm ( 4 . 7 2 ~ 1 0 - ~ m3/s). The last 3 minutes consisted of water only, and served as an air purge. The following parameters were monitored continuously with field instrumentation: influent and effluent turbidity, feedwater flowrate, pressure differential across the filter, and chlorine residual up and downstream of the CCC. Lab personnel at SEWPCP performed the following analyses on daily grab samples of filter influent and effluent: TSS (mg/l), pH, alkalinity (mg/l as Ca C03), TDS (mg/l), and BOD5 (mg/l). TDS and BOD5 analyses were done daily until May 13, and biweekly thereafter. Coliform (MPN) analyses were performed daily on grab samples of the CCC effluent. All analyses were performed according to Standard Methods5. Experiments. Over one hundred filter runs were completed and analyzed. Tests were conducted from February to September 1992, during both dry and wet weather conditions. Tests were divided into five main categories : I. Title 22 Continuous Operation Two testing periods were devoted to proving that Title 22 unrestricted use requirements could be met continuously using In-line Filtration. The first period, March I to March 19, was at the beginning of the study, and the second, June 26 to July 14, was in the middle of the study. During these tests, the filter was left undisturbed, except for routine maintenance and sample collection. Filter runs were automatically terminated by headloss (HL) of 76" across the filter bed. 11. Alum Optimization Tests to determine the optimum alum dosages were conducted from March 26 to May 31. Two different types of experiments were performed. For the first set of experiments, filter runs were short (approximately 2 hours). This allowed time for the effluent turbidity to stabilize while observing filter performance on a clean media bed. This was interpreted as the maximum expected removal efficiency of the filter for a particular alum dose. After the effluent turbidity stabilized, a manual backwash cycle was Thitiated manually, and the alum

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d o s e changed. These t e s t s narrowed t h e xange o f alum d o s e s w h i l e r e d u c i n g f i l t e r r u n time f o r e a c h e x p e r i m e n t . R e s u l t s are n o t shown. For t h e second set o f experiments, f i l t e r r u n s w e r e t e r m i n a t e d by a n a u t o m a t i c backwash a t a p r e s s u r e d r o p o f 76" a c r o s s t h e f i l t e r . T h e s e t e s t s c o r r e l a t e d e f f l u e n t quality with influent t u r b i d i t y a t a particular alum d o s a g e . These e x p e r i m e n t s w e r e p e r f o r m e d on e i t h e r SEWPCP s e c o n d a r y e f f l u e n t , o r a s i m u l a t e d h i g h s o l i d s l o a d i n g (HSL) f e e d w a t e r ( a 1:l mixture of secondary e f f l u e n t and r e t u r n a c t i v a t e d s l u d g e ) w i t h t u r b i d i t i e s r a n g i n g from 7 t o 1 2 NTU. Although t h e S t a t e o f C a l i f o r n i a may requj-re a d d i t i o n a l t r e a t m e n t f o r f e e d w a t e r t u r b i d i t y g r e a t e r t h a n 10 NTU, t h i s a l l o w e d e v a l u a t i o n o f f i l t e r and c o a g u l a n t range of influent performance over a broader c o n d i t i o n s . I f T i t l e 22 s t a n d a r d s can be met w i t h t h e s e h i g h e r t u r b i d i t i e s , there i s a g r e a t e r a s s u r a n c e t h a t t h e s e same s t a n d a r d s w i l l be m e t w i t h feedwater t u r b i d i t y within t h e allowable range. 111. Polymer a d d i t i o n E x p e r i m e n t s w i t h a c a t i o n i c medium w e i g h t polymer (Nalco 8102) were performed between June 1 and June 1 0 u s i n g HSL f e e d w a t e r w i t h t u r b i d i t i e s r a n g i n g from 6 . 5 t o 1 2 N T U . Polymer was i n j e c t e d i n t o t h e f e e d l i n e i m m e d i a t e l y u p s t r e a m of t h e f i l t e r . C o n s t a n t alum and polymer d o s e s w e r e m a i n t a i n e d t h r o u g h o u t t h e l e n g t h o f each r u n which w e r e t e r m i n a t e d a t a HL o f 7 6 " . Alum d o s e s r a n g e d between 2 . 5 and 8 . 8 m g / l , w h i l e polymer These r u n s d o s e s ranged from 0.2 t o 0 . 5 mg/l. c o r r e l a t e d e f f l u e n t t u r b i d i t y with i n f l u e n t t u r b i d i t y and h e a d l o s s a c r o s s t h e f i l t e r .

C o n c u r r e n t l y , w i t h e x p e r i m e n t s I - 111 a d i s i n f e c t i o n s t u d y a s s e s s e d t h e e f f e c t i v e n e s s of t h e c h l o r i n e c o n t a c t channel. P i l o t p l a n t e f f l u e n t w a s monitored d a i l y f o r c h l o r i n e r e s i d u a l and c o l i f o r m l e v e l s f o r t h e d u r a t i o n o f t h e s t u d y , from March to J u l y . I V . Chlorinated feed From J u l y 1 4 u n t i l J u l y 28, c h l o r i n a t e d f i n a l e f f l u e n t was f e d t o t h e p i l o t f i l t e r to s t u d y t h e e f f e c t o f c h l o r i n e on f i l t e r p e r f o r m a n c e . T h i s f e e d w a t e r , which i s used as p l a n t p r o c e s s w a t e r , c o n t a i n e d a h i g h c h l o r i n e r e s i d u a l (15-23 mg/l) i n o r d e r to m e e t T i t l e 22 r e s t r i c t e d u s e s t a n d a r d s .

Two t y p e s o f t e s t s w e r e performed: Two-hour c l e a n bed t e s t s f o l l o w e d by a manual backwash, a n d c o m p l e t e f i l t e r r u n s t e r m i n a t e d by a u t o m a t i c backwash a t a HL o f 76 i n c h e s . The d o s e s w e r e k e p t c o n s t a n t t h r o u g h o u t e a c h t e s t . Chemical d o s e s u s e d were t h o s e fourid o p t i m a l w i t h u n c h l o r i n a t e d feed.

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V . Adsorption C l a r i f i c a t i o n

c l a r i f i e r upset t h a t occurred during t h i s study r e s u l t e d i n SEWPCP secondary e f f l u e n t t u r b i d i t i e s o f 20 NTU. Also, s h o r t term t u r b i d i t i e s of t h i s magnitude are n o t uncommon d u r i n g w e t w e a t h e r . T h e r e f o r e , i t w a s decided t o i n v e s t i g a t e whether t h e Adsorption C l a r i f i c a t i o n p r o c e s s c o u l d meet T i t l e 22 r e q u i r e m e n t s when i n f l u e n t t u r b i d i t i e s w e r e between 12 and 20 NTU.

A

Two MULTIWASB f i l t e r s w e r e r u n i n s e r i e s . The f i r s t f i l t e r was u s e d a s a c o a r s e f i l t e r , w i t h a n e x p e c t e d e f f l u e n t t u r b i d i t y o f l e s s t h a n 1 0 NTU. The s e c o n d f i l t e r would p r o v i d e t h e f i n a l p o l i s h i n g r e q u i r e d t o m e e t T i t l e 22 e f f l u e n t s t a n d a r d s . They w e r e l o a d e d w i t h 3 . 5 mm and :1.5 mm e f f e c t i v e s i z e a n t h r a c i t e media, r e s p e c t i v e l y . The f i l t e r area and bed d e p t h w e r e 0.54 s q f t ( 0 . 0 5 m 2 ) and 48“ (1.22 m ) f o r t h e c o a r s e f i l t e r , and 0 . 4 4 s q f t . ( 0 . 0 4 m 2 ) and 30” ( 0 . 7 6 m ) f o r t h e f i n e filter

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T e s t s w e r e c o n d u c t e d i n August 1992, and f o c u s e d on o p t i m i z i n g alum and c a t i o n i c polymer d o s e s f o r feedwater t u r b i d i t i e s i n t h e 12-20 NTU r a n g e . Chemicals w e r e i n t r o d u c e d b e f o r e t h e c o a r s e f i l t e r where f l o c c u l a t i o n w a s promoted by t h e t u r b u l e n t f l o w e n e r g y a s it p a s s e d t h r o u g h t h e bed. F i l t r a t i o n r a t e w a s m a i n t a i n e d a t 5gpm/sqft ( 6 . 3 ~ 1 0 - m ~/s) i n the fine f i l t e r b u t v a r i e d i n t h e c o a r s e f i l t e r . The backwash c y c l e f o r e a c h f i l t e r was i n i t i a t e d s e p a r a t e l y . I n t h e c o a r s e f i l t e r , a u t o m a t i c backwash o c c u r r e d a t a t e r m i n a l heaclloss o f 6 0 ” ( 1 . 5 2 m ) , w h i l e i n t h e f i n e f i l t e r , backwash w a s s t a r t e d manually a s needed. Coarse and f i n e f i l t e r e f f l u e n t t u r b i d i t i e s , f e e d w a t e r f l o w r a t e and d i f f e r e n t i a l p r e s s u r e a c r o s s t h e c o a r s e Influent f i l t e r were m o n i t o r e d c o n t i n u o u s l y . turbidities, feedwater f l o w r a t e and d i f f e r e n t i a l p r e s s u r e a c r o s s t h e f i n e f i l t e r were m e a s u r e d p e r i o d i c a l l y d u r i n g t h e day.

Results

and

diclcusclion

T i t l e 22 c o n t i n u o u s o p e r a t i o n . Continuous o p e r a t i o n o f the f i l t e r demonstrated t h e a b i l i t y of Inline Title 22 u n r e s t r i c t e d u s e F i l t r a t i o n t o meet

r e q u i r e m e n t s c o n s i s t e n t l y and r e l i a b l y o v e r b o t h d r y and w e t w e a t h e r c o n d i t i o n s . Table 3 p r e s e n t s i n f l u e n t and e f f l u e n t t u r b i d i t i e s and d a i l y alum d o s e s . Maximum h o u r l y i n f l u e n t t u r b i d i t y w a s a l m o s t 1 9 NTU, a l t h o u g h maximum hour1.y e f f l u e n t t u r b i d i t y w a s l e s s t h a n 4 . 6 NTU, below t h e 5.0 NTU maximum set by T i t l e 22. On 6 / 2 9 a v e r a g e e f f l u e n t t u r b i d i t y w a s 2 . 7 NTU. F o r a s u s t a i n e d period of t i m e i n f l u e n t t u r b i d i t i e s reached o c c u r r e d a f t e r r e g u l a r working h o u r s , s o 10 N T U . T h i s t h a t alum a n d polymer d o s e s c o u l d n o t b e a d j u s t e d chemical accordingly. In a f u l l scale f a c i l i t y , 235

addition would be automatically controlled by influent turbidity and lower effluent turbidities would be expected in response to more appropriate chemical dosages. Figure 3 presents a typical 48-hour period. Effluent turbidity is kept well below 2 NTU, regardless of the

influent quality and headloss build-up. This suggests that when appropriate chemical addition is used with Inline Filtration, complete destabilization of influent particles results, and a consistently c3ood tertiary effluent quality is possible. Throughout the Tiitle 2 2 continuous operat.ion, effluent chlorine dose was maintained at 10 mg/l. The resulting chlorine residuals ranged from 5 . 2 t:o 8.0 mg/l. Coliform counts were always less than 2 cfu/100 ml. Similar levels of treatment resulted in a 5-109 removal of seeded viruses6. In a 10 year monitoring program, only 1 of 590 monthly samples tested positive for enteric viruses. This suggests that Title 2 2 standards represent an adequate approach t o consistently minimizing health risks associated with the use of reclaimed water7. Moreover, there have not been any reported cases of illness resulting from the use of reclaimed water in St. Petersburg, Florida, nor any chiinges in the epidemiologic patterns of aseptic meningitis and hepatitis A, historically associated with waterborne t r a n s m i s s i o n 8 . Indeed, a recently published9 epidemiologic study on morbidity levels associated with the use of reclaimed water in irrigation of public spaces found that there was no difference in gastrointestinal illnesses between users of parks watered with potable water versus those watered with reclaimed water when fecal coliform counts were less than 500/lOO ml, and symptoms were probably more the result of endotoxins than to the presence of viable microorganisms.

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Alum optimization. Alum doses tested ranged from 0 t o 7.4 mg/l with influent turbidities in the 1.9 to 1 2 . 0 NTU range (See Table 4 ) . For influent turbidities of 7 . 0 NTU or higher, In-Line Filtration with alum addition alone, ‘did not consistently reduce effluent turbidities to Title 2 2 values. Some occasional successful runs occurred, however, which can be explained by the heavy dependence of suspended solids removal on particle size. That is, it is assumed that the successful runs occurred when higher turbidities occurred in combination with a high proportion of larger particle sizes, rather than as a result of particle destabilization.

236

For lower .influent turbidities, however, the process was very efficient when particle destabilization was complete (:See F i g u r e 4 ) . Turbidity removals between 7 5 and 05% and runs of more than 30 hours were achieved with alum closes between 2 . 4 and 2 . 0 mg/l for influent turbidities ranging from 5 to 7 NTU. These filtration run lengths fall within the upper end of the economical range €or this type of application.1° Further increases in run length would n o t result in significantly higher savings. Headloss gradients across the filter asuggestedthat the entire depth of media bed was utilized and that the filter was used near capacity. The absence of turbidity breakthrough also indicates an appropriate chemical dosage was used as well as an optimal filter run length. Suspended solids and turbidity removals of 66 to 7 5 per cent are typical for filters following biological secondary treatmentll. Filter performance was very dependent on alum dose. Optimal doses were found to be between 2 and 3 mg/l, and when alum doses were below or above this range, turbidity removals decreased. It is possible that influent particles were only partially distabilized and aggregated, thus their tendency to remain in suspension. With higher influent turbidities, i.e. between 5 and 7 NTU, turbidity breakthrough would occur in those circumstances, and Title 2 2 requirements could not be met. Therefore, for a successful full scale application of In-Line Filtration, close monitoring of influent turbidity and prompt response t o fluctuations will be crucial. Polvmer addition. A limited number of tests were conducted with polymer addition. T a b l e 5 compares alum addition with alum and polymer addition, for similar influent turbidities. Polymer addition appears t o promote greater removal efficiencies. With alum alone, average influent turbidity was 0 . 0 NTU and effluent turbidity was 2 . 7 NTU. With alum and polymer addition, these values were 0 . 4 and 1.7 NTU, respectively, a 15% increase in turbidity removal. Polymer addition reduced run times fxom an average of 2 0 . 7 hours to 16.3 hours, a reduction of 21%. From direct observation, polymer addition seemed t o enhance floc: strength which allowed it to bridge across filter grains, and form a shallow sieve that produced a good quality effluent at the expense of increased headloss. For high turbidities ( 7 . 0 10.0 NTU), however, polymer addition is necessary for In-Line Filtration. When used on feedwater in the 0 - 7 NTU influent turbidity range, polymer addition results in a more consistent and easier to operate, albeit less efficient, process.

237

Experiments performed w i t h t h e Adsorption C l - a r i f i c a t i o n p r o c e s s w i t h i n f l u e n t t u r b i d i t i e s between I and 1 0 NTU found s i m i l a r c o m b i n a t i o n s of alum and polymer d o s e s r e s u l t e d i n h i g h e r t u r b i d i t y r e m o v a l s . Although t h i s p r o c e s s would b e more c o m p l i c a t e d to o p e r a t e , it proved c a p a b l e of b r i n g i n g i n f l u e n t t u r b i d i t i e s a s h i g h a s 1 0 NTU to w i t h i n T i t l e 2 2 r e q u i r e m e n t s , e x p a n d i n g t h e f e e d w a t e r r a n g e t h a t c o u l d be u t i l i z e d w i t h I n - L i n e Filtration. T u r b i d i t y removals i n t h i s s t u d y a g r e e w i t h r e s u l t s of a study12 conducted by Marin Municipal Water D i s t r i c t . That s t u d y used t h e Adsorption C l a r i f i c a t i o n p r o c e s s following a two-stage, high-rate tricklting f i l t e r p r o c e s s to produce a n e f f l u e n t w i t h t u r b i d i t i e s i n t h e 1 0 to 2 0 NTU r a n g e . The r e p o r t e d alum and polymer ( u n s p e c i f i e d ) d o s e s w e r e 3 to 4 t i m e s h i g h e r t h a n t h o s e f o u n d i n t h i s s t u d y , p e r h a p s r e l a t e d to t h e h i g h e r p r o p o r t i o n o f p a r t i c l e s s i z e d 2 p.m o r l e s s a s s o c i a t e d with t r i c k l i n g f i l t e r s . BY eliminating coagulation and clarification f a c i l i t i e s , a substantial reduction i n t h e foot-print is of t h e f u l l s c a l e water reclamation plant a n t i c i p a t e d . Furthermore, chemical doses f o r f u l l t r e a t m e n t r a n g e from I 5 to 250 mg/l of alum and 2 to 20 mg/l of p o l y m e r l o , many t i m e s g r e a t e r t h a n t h e o p t i m a l d o s e s f o r In-Line F i l t r a t i o n found i n t h i s s t u d y .

run l e n a t h . F i l t e r run t i m e s w e r e n o t g r e a t l y a f f e c t e d by e i t h e r alum d o s e o r i n f l u e n t t u r b i d i t i e s below I NTU. Average r u n t i m e was 2 9 h o u r s f o r a l l t e s t s m e e t i n g T i t l e 2 2 r e q u i r e m e n t s , and also for t h o s e w i t h o p t i m a l alum d o s e s , s u g g e s t i n g t h a t t h e f i l t e r ' s p o t e n t i a l f o r removing s o l i d s was c l o s e to capacity.

Filter

I n c r e a s e d i n f l u e n t t u r b i d i t y (above I NTU), reduced run l e n g t h to an a v e r a g e o f 2 0 . 7 h o u r s f o r t e s t s m e e t i n g T i t l e 2 2 r e q u i r e m e n t s . The i n c r e a s e d s o l l i d s l o a d i n g a p p e a r e d to e x h a u s t t h e f i l t e r ' s c a p a c i t y f a s t e r . The a d d i t i o n o f polymer f u r t h e r r e d u c e d t h e a v e r a g e r u n l e n g t h by p r o d u c i n g s t r o n g e r f l o c s which d i d n o t p e n e t r a t e t h e e n t i r e media bed d e p t h . T h i s r e s u l t e d i n an a v e r a g e r u n l e n g t h of 1 6 h o u r s . The r e d u c t i o n i n r u n l e n g t h h a s a modest e f f e c t on f i l t e r down-time and backwash w a t e r volume. Thus, a t an a v e r a g e r u n l e n g t h of 2 9 h o u r s , t h e p e r c e n t a g e o f backwash volume o v e r t o t a l r u n volume i s 1 . 2 5 % . and i n c r e a s e s to 2 . 2 0 % when t h e a v e r a g e r u n l e n g t h i s 1 6 hours. T h i s i s less t h a n a one p e r c e n t i n c r e a s e i n backwash volume. These r e s u l t s f a l l i n t h e range of 0 . 3 t o 3% r e g a r d e d as o p t i m a l 1 3 . S i m i l a r l y , downtime i n c r e a s e s from 0 . 5 2 % to 0 . 9 4 % which t r a n s l a t e i n t o 45 and 0 2 h o u r s of downtime i n a y e a r . 238

Disinfection effectivenesa Disinfection effectiveness was monitored continuously for 17 weeks. Chlorine doses ranged from 4 t o 12 mg/l, and chlorine residuals from 0.6 t o 9.5 mg/l. Coliform counts of less than 2.2/100 ml were consistently achieved with chlorine residuals of 2.1 mg/l (Ct value of 340 mg.min/l) or greater. Chlorine residuals range from 4 to 6 mg/l with a 90 min contact time (Ct values of 360 to 540 mg.min/l) in six Los Angeles County wastewater reclamation plants, while the City of S t Petersburg reports a chlorine residual of 4 mg/l. Both meet or exceed current disinfection requirements. In this context, the 5 mg/l chlorine residual in combination with a 2-hour hydraulic residence time required in Title 22 appears conservative. Chlorinated feed. Filter performance was inadequate with chlorinated feed. Influent turbidities ranged from 2.4 to 5.0 NTU while effluent turbidities varied from 2.1 to 4.5 NTU, and in some instances, the effluent had a higher turbidity than the influent. Although no change in pH was evident, chlorine prevented or inhibited coagulation and flocculation. Relatively low headloss gradients (0.60-1.15 inch/hour) were indicative to€ poor solids removal. Since the use of moderately chlorinated feed (chlorine residuals up to 5 mg/l) in granular media tertiary filters is well documented7 9 1 l4 , this inhibition might be related t o the high chlorine content in the feedwater used in these experiments. The mechanism was not identified. Further tests will be necessary t o determine whether chlorinated pure-oxygen activated sludge secondary effluent can be used as feed for a water reclamation plant.

Con c lu s ion1s This study proved that Title 22 standards can be met using 1n-Li.ne Filtration on pure-oxygen activated sludge secondary effluent. Alum doses of less than 10 mg/l in combination with polymer doses of less than 0.5 mg/l were needed. Title 22 standards were met with influent turbidities as high as 12 NTU, while the 95 percentile secondary effluent turbidity at SEWPCP was 9 NTU in 1988-91. However, during storm conditions, influent turbidities of up t o 2 0 NTU were observed. The Adsorption Clarification process proved capable of meeting Title 22 requirements with these high feedwater turbidities, so that flocculation and sedimentation facilities may still be eliminated. In any full scale plant, chemical addition should be controlled aLutomatically,the dosage based on influent turbidities t o the filter. The set point and ranges

239

would b e d e t e r m i n e d d u r i n g s t a r t - u p facility.

of

EL

f u l l scale

I n J a n u a r y 1994, DOHS approved d e s i g n of a f u l l s c a l e . f a c i l i t y u s i n g I n l i n e F i l t r a t i o n b a s e d on t h e r e s u l t s presented i n t h i s paper. The p r o c e s s w a s approved f o r high public contact i r r i g a t i o n , f i r e fighting, t o i l e t f l u s h i n g and washdown/cleaning. Predesign of a f u l l scale r e c l a m a t i o n p l a n t w i l l b e g i n i n 1995.

.

AC kno w 1e du-

The a u t h o r s would l i k e t o r e c o g n i z e t h e Bureau o f E n g i n e e r i n g , Department o f P u b l i c Works, C i t y a n d County o f San F r a n c i s c o f o r t h e f i n a n c i a l s u p p o r t which made t h i s work p o s s i b l e , a n d t h a n k t h e p e r s o n n e l o f t h e Bureau o f Water P o l l u t i o n C o n t r o l f o r t h e i r d e d i c a t e d a s s i s t a n c e and c o - o p e r a t i o n d u r i n g t h i s p r o j e c t . C a r o l y n Chiu a n d D a n i e l Mamais c o n d u c t e d t h e t e s t s w i t h t h e Adsorption C l a r i f i c a t i o n p r o c e s s . REFERENCES 1. Lejano, R . P . , G r a n t , F.A. , Richardson, T . G . , Smith, B . M . , and Farhang, F. ( 1 9 9 2 ) . A s s e s s i n g t h e B e n e f i t s of

Water Reuse. Water Environ. Technol.

r

8, 44

2 a . C a l i f o r n i a A d m i n i s t r a t i v e Code, T i t l e 22, D i v i s i o n 4 ( 1 9 7 8 ) . S t a t e of C a l i f o r n i a , D e D artment of Health S e r v i c e s , Berkeley, CA 2b. T i t l e 22 F i n a l R e v i s i o n ( 1 9 9 3 ) . S t a t e of C a l i f o r n i a , Devartment o f H e a l t h S e r v i c e s , Berkeley, CA 3 . Asano, T . , C r i t e s , R . D . , a n d Tchobanoglous, R.W. ( 1 9 9 2 ) . E v o l u t i o n o f T e r t i a r y Treatment Requirements i n C a l i f o r n i a . Water Env i r o n . T e c h n o Lr 4 , 36 4 . P o l i c y S t a t e m e n t f o r Wastewater Reclamation P l a n t s w i t h Direct F i l t r a t i o n (1988). S t a t e of C a l i f o r n i a , D e D a r t ment o f H e a l t h S e r v i c e a , Berkeley, CA

5 . S t a n d a r d Methods f o r t h e Examination o f Water a n d W a s t e w a t e r ( 1 9 9 1 ) . 1 8 t h e d . , Am. P u b l i c H e a l t h Assoc., Washington, D C .

.

6 . Miele, R . P . ( 1 9 7 7 ) . Pomona V i r u s Study F i n a l R e p o r t . C a l i f . S t a t e Water R e s . C o n t r o l Board a n d U S EPA, Sacramento, CA

7.Yanko, W . A . ( 1 9 9 3 ) . A n a l y s i s o f 10 Years o f V i r u s M o n i t o r i n g D a t a from Los A n g e l e s County T r e a t m e n t P l a n t s Meeting C a l i f o r n i a Wastewater Reclamation C r i t e r i a . Water Environ. Res, 3, 221

240

8 . Crook, J . , a n d J o h n s o n , W . D . (1991). H e a t h a n d W a t e r - Q u a l i t y C o n s i d e r a t i o n s w i t h a Dual Water System. m e r Enviaxm. T e c h I l Q L , 8 , 13

9 . Schwebach, and Michael, Perspectives.

G . H . , C a f a r o , D . , Egan, J . , G r i m e s , M., G. (1988). Overhauling Health E f f e c t s W , 4, 4 7 3

1 0 . Burns, D. ( 1 9 9 2 ) . P e r s o n a l Communication. Ames, I A 11. Water

Reuse

m, A l e x a n d r i a ,

GFC I n c ,

( 1 9 8 9 ) . Task F o r c e on Water R e u s e . VA

1 2 . F a l l e r , J.A. , and Ryder, R.A. ( 1 9 9 1 ) . C l a r i f i c a t i o n and F i l t r a t i o n t o M e e t Low T u r b i d i t y Reclaimed Water S t a n d a r d s . Water Environ. Technol., 1, 68 1 3 . Fox, R . L . ( 1 9 7 2 ) . Advanced Wastewater T r e a t m e n t Using Alum w i t h Direct F i l t r a t i o n . Yniv. o f Celom, Boulder, CO 14.Lauer, W.C., R o g e r s , S . E . , Lachance, A . M . , and ( 1 9 9 1 ) . Process Selection f o r Potable Nealey, M . K . Reuse H e a l t h E f f e c t s S t u d i e s . Journal, 11, 52

241

Figure 1. Tertiary Treatment Processes Full Treatment Clarification

media filtration

CI,

IIIIIt-

Reclaimed wastewater

Chlorine contact basin

Direct Filtration

mix

media filtration

ci2

5 ++~Illlt-

Reclarmed wastewater

Chlorine contact basin

In-Line Filtration

,--

Alum Polymer

&

Secondary Secondary effluent

Rapid mix

n c12

-

Reclaimed x ~ l Chlorine l l contact l l l ~ wastewater Granular basin media filtration

,/ I

242

Figure 2. Pilot Filter Flow Schematic

Figure 3. Typical 48 Hours During Continuous Operation

12 E

-

10

80

1 4

70 60' 50 t3

5

p 6

40: 30

g 4

20

9 -E

or

2

0

'

4

7 =

10 8

12

16

20

28

24

32

'"0 36

40

44

48

T i e bow)

80

6

70 2 60$

50

8 4

3 m

30% 20 g 10 0 Time (hour)

-Influent

-Effluent

-------- Title22 -Headlos

244

0

. =. . .

I

1’0

0

0 0

0

c7

W

.

0

6‘0 I

1

-

ITable 1. Feedwater Characteristics WI kly Averages Tss BODSTurbidity Dates (NTU) (mg/L) (mg1L.L

3109-3113 311 6-3/20 3/23-3127 3/30-4103 4/06-4/10 411 3-4117 4120-4124 4/27-5/01 5104-5/08 511 1-5115 511 8-5122 5/26-5129 6101 -6105 6/08-6112 611 5-611 9 6/22-6126 6/29-7102 7/06-7/10 711 3-7114

5.7 5.8 6.8 6.5 5.9 4.8 3.7 6.8 9.6

7.3 7.9 6.1 8.2 9.8

3.8 2.1 1.8 6 9.8 1.8

23 20 27

l d

If 1:

47

1(

33 26 21 23 24 26 27 31 32 19 17 20 27 26 18 25

1: 14

5

-

E

-

-

-

1: Average 47 1! Maximum 17 I Minimum Results are t sed on daily grab samples, except influent turbidity which is- a-24-hour-average

246

Table 3. Continuous Operation (24 hour Averages)

Day 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29

Alum

4.8 4.7 4.8 4.9 5.8 7.3 6.8 6.0 6.1 5.4 4.2 2.2 1.8 1.7 4.6 3.5 3.2 2.2 1.6 2.2 1.6 1.4 2.8 2.7 1.8 1.3 1.7 1.9

2.6 2.6 2.4 2.8 3.6 4.6 3.8 2.0 3.2 2.8 2.8 1.3 1.2 1.2 2.0 2.2 1.8 1.5 0.4 1.o 1.o 1.2 1.6 1.4 1.o 1.O 0.8 0.7

8.8 7.2 7.2 7.0 11.4 18.8 12.8 12.8 9.8 9.2 6.1 5.6 3.2 6.0 10.4 7.2 8.4 6.0 3.6 8.4 2.8 2.0 5.4 7.0 3.6 2.0 6.8 3.6

0.9 1.o 0.9 0.9 1.1 1.7 1.3 1.o 0.9 1.3 1.6 1.5 1.3 1.2 2.7 1.9 1.4 0.7 0.7 0.7 0.9 1.2 1.1 0.9 0.9 0.9 0.6 1.0

248

0.7 0.8 0.8 0.8 0.9 1.1 0.8 0.8 0.7 0.8 1.3 1.2 1.o 1.o 1.2 0.9 1.o 0.6 0.6 0.6 0.7 0.8 0.8 0.8 0.7 0.7 0.5 0.7

2.4 1.8 1.1 1.1 2.2 3.4 2.9 2.4 1.2 2.0 1.9 2.2 2.0 1.5 4.8 3.1 2.2 1.o 1.o 0.8 2.6 1.8 1.4 1.3 1.1 1.1 1.2 1.4

(mg/L] 2.4 2.3 2.5 2.4 2.4 2.5 2.5 2.4 2.4 2.4 2.5 2.1 2.4 2.5 2.3 2.2 3.0 2.6 3.5 3.4 2.7 2.7 2.7 2.8 2.6 2.6 2.6 2.6 2.5

timlzz

able Alum Dose

mg/L:

Mluent

1.2 1.4 1.4

1.9 3.P 3.4

1.5

N

%i

rermina jeadlos

2.2 2.4 2.4 2.5 2.8 3.8 4.5 5.4 5.4 5.7 6.2 6.6 0.0 0.0

0.9 1.2 1.4 1.5 2.1 2.1 2.2 2.4 2.4 2.4 2.5 2.6 2.7

-

9 7

e . ,

4.8 4.7 4.5 4.9 4.8 4.8 3.4 4.9 2.4 4.5 3.4 4.4 6.6 6.6 5.8 6.8 6.4 5.5 6.8 6.9 6.4 6.2 5.9 5.9 5.9 5.6 6.1

1.4

Run Time

1.6 0.8

75

9”

76 76 76 76 76 76 46 37 76 76 76 76 56 59 44 76 36 76 76 76 29 76 76 76 76 76 76

41 30 30 30 22 14 20 34 26 26 24 21 24 24 19 22 15 26 18 24 22 30 25 34 30 23 41

1.4 0.9 0.9 0.9 1.2 1.9 1.6 2.2 1.9 2.1 1.8 2.1 1.4 2.0 1.5 2.1 1.3 2.3 1.8 1.8 2.0 0.8 1.0 1.0 1.2 1.4 2.4 -

Alum

DO%?

21 26 23

-

l’urbidl t]

rermini lead108

m

Run Time

AH

hadier

(hour) (in/htl (mg/Ll Influent Efflueni - Qnches -

(inches) (hour) (in/y 76 76 51

1.1

rable - Cont‘d

AH ;radien 3.6 2.9 2.3

2.8 2.8 2.8

6.8 6.1 6.3

nn

2.9

6.5

1.8 2.6 2.6 2.6 3.5 5.4 2.3 1.1 2.9 3.0 3.2 3.6 2.4 2.5 2.4 9.5 2.4 3.0 4.3 3.2 1.3 2.5 3.0 2.2 2.6 3.3 1.8

3.7 4.0 4.7 4.8 5.0 5.2 7.0 1.6 2.3 2.3 2.4 2.4 2.5 3.0 3.2 3.2 3.5 3.6 4.4 4.7 5.6 5.6 6.8 7.4

5.8 6.6 6.7 6.7 6.5 7.0 5.6 12.0 7.5 7.1 8.4 9.8 7.3 7.1 11.9 10.4 7.2 7.7 8.6 9.2 10.0 12.0 7.3 11.5 5.0 1.9 6.9

Y.Y

Average

Minimum Maximum

0.0 6.6

-

2.8 1.1 1.2 2.6 1.4 3.7 2.2 2.2 2.8 3.6 1.9 3.1 2.5 2.0 1.9 4.5 2.5 2.7 4.0 3.0 2.2 0.6 1.0 2.1 2.8 4.3 2.8 3.8 1.6 0.8 2.4 -

40 76 76

I ^

IO

76 76 76 76 69 76 41 76 76 76 76 62 76 52 71 62 76 76 76 76 76 53 64 76

22 26 26 34 18 41 21 20 21 61 16 14 22 14 24 19 27 19 23 24 15 24 14 19 22 16 24 17 26 14 41

1.8 2.9 2.9 2.3 4.2 1.8 3.7 3.8 3.3 1.9 2.6 5.4 3.5 5.6 3.2 3.4 2.9 2.a 3.1 2.6 5.1 3.2 5.4 4.0 3.5 3.3 2.6 4.4 2.8 1.1 5.4

---

I

I Headloss I RunTime

(mglL) 0.20 0.21 0.21 0.25 0.29 0.29 0.31 0.35 0.47 0.48

2.6 3.6 2.5 8.3 8.8 8.8 3.6 7.2 4.3 2.5

8.7 8.1 7.5 8.3 12.0 7.1 6.5 9.4 6.7 8.7

1.7 1.5 1.3 1.3 1.0 1.8 1.6 2.1 1.7 2.3

2.50 8.80

250

76 76 76 76 76 76 76 76 76 76

13 17

15 17 18 15 15 19 25 15

hH Gradienl (in/hr) 5.2 6.0 4.5 5.2 4.5 4.3 5.1 5.0 3.9 3.1 4.9 4.7 3.1 6.0